Ab exercises you can do using a stability ball. Ab exercises you can do using a stability ball.

Ball Trunk Rotation with 1 Leg

Stability Ball Ab Exercises
Primary Muscle Group: Obliques

Muscle Groups Worked in This Exercise:  Obliques and Rectus Abdominis

Preparation: Position yourself sitting on a stability ball with your knees bent at 90 degrees and used to balance your body on the ball.  Hold a single dumbbell in both hands positioned in your mid core area close to your body and elbows bent outward.

Breathing:  Breath out on the contraction of the muscle and breath back in on the way back to the start position.

Ball Russian Twist

Stability Ball Ab Exercises
Primary Muscle Group: Abdominals

Muscle Groups Worked in This Exercise: Lower Back

Preparation: Roll out onto ball in a supine position. The ball should be on your upper back. Keeping your hips and body parallel to the floor (no sagging of the hips) rotate your shoulders to the right with your arms extended. Remember to keep your trunk parallel with the floor.

Ball Pike Reach

Stability Ball Ab Exercises
Primary Muscle Group: Abdominals

Preparation: Lie on your back and place your arms at your sides with your palms facing the floor. Grasp the ball between your calves with your legs extended.

Breathing: Exhale as you curl up.

Ball Oblique Twist Advanced

Stability Ball Ab Exercises
Primary Muscle Group: Core Muscles

Muscle groups worked in this exercise: Rectus Abdominus, Internal and External Obliques.

Preparation: Start by sitting on the ball with your knees bent and feet flat on the floor. Slowly walk your feet forward as you slide your torso down the ball. Your trunk should be parallel to the floor. Just let your hips clear the ball and let your lower back press into the ball; cross your arms over your chest.

Breathing: Exhale as you lift. Inhale as you relax back to starting point.

Ball Crunch Super

Stability Ball Ab Exercises
Primary Muscle Group: Core Muscles

Muscle groups worked in this exercise: Upper and Lower Abdominals

Preparation: Start by sitting on the ball with your knees bent and feet flat on the floor. Slowly walk your feet forward as you slide your torso down the ball. Your trunk should be parallel to the floor. Just let your hips clear the ball and let your lower back press into the ball; cross your arms over your chest.

Breathing: Exhale as you lift. Inhale as you relax back to starting point.

Ball Crunch Advanced

Stability Ball Ab Exercises
Primary Muscle Group: Core Muscles

Muscle groups worked in this exercise: Upper and Lower Abdominals

Preparation: Start by sitting on the ball with your knees bent and feet flat on the floor. Slowly walk your feet forward as you slide your torso down the ball. Your trunk should be parallel to the floor. Just let your hips clear the ball and let your lower back press into the ball; cross your arms over your chest.

Breathing: Exhale as you lift. Inhale as you relax back to starting point.

Ball Bottoms-Up

Stability Ball Ab Exercises
Primary Muscle Group: Quadriceps femoris, Gluteus, Abdominals

Muscle Groups Worked in This Exercise: Gluteus, Bicep Femoris

Preparation: Lie on the floor with your arms down at your sides, palms down. Your heels and calves should rest on the top of the ball.

Breathing: Exhale while you raise your hips, inhale when you release the position back to the floor.

Ball Band Lateral Raise Intermediate

Stability Ball Ab Exercises
Primary Muscle Group: Shoulders

Muscle Groups Worked in This Exercise: Trapezius, Deltoideus (anterior and middle)

Preparation: Sit on the ball, keeping your back straight, your abs tight and secure an exercise band under your right foot. Raise and extend your left foot. Grasp the band in both hands and fully extend your arms by your hips. Palms should be facing the ball.

Breathing: Exhale when raising arms, inhale when lowering to start.

Ball Balanced Roll Ups

Stability Ball Ab Exercises
Primary Muscle Group: Core Muscles

Muscle groups worked in this exercise: Upper and Lower Abdominals

Preparation: Lie on the floor with your arms down at your sides, palms down. Your heels and calves should rest on the top of the ball.

Breathing: Exhale as you lift. Inhale as you relax back to starting point.

Ball Reverse Curls

Stability Ball Ab Exercises

Primary Muscle Group: Abdominals

Preparation: Lie on your back and place your arms at your sides with your palms facing the floor. Grasp the ball between your calves with your legs extended.

Breathing: Inhale to grasp the ball, exhale after exercise.

Ball Plank Advanced

Stability Ball Ab Exercises

Primary Muscle Group: Core Muscles

Muscle groups worked in this exercise: Abdominus Rectus, Internal and External Obliques, Triceps

Preparation: Kneel on the floor with the ball about a foot in front of you. Both forearms are placed upon the top of the ball, palms together and fingers interlaced. Pull your navel up close to your spine.

Breathing: Exhale as you lift your knees, Inhale when you return knees to the floor. Breathe normally while holding the plank position.

Ball Crunch Obliques

Stability Ball Ab Exercises
Place ball at low back area and place feet wide to stabilize the body. Cross arms over chest. In a controlled motion, keeping neck straight, curl upper body up while turning your torso to the left. Contract abdominals fully without compromising form. While maintaining the controlled motion, return to starting position. Do not allow muscle to relax before next repetition. After completing one set on the left, switch to your right side. Focus on really twisting your torso and feeling the contraction when you are in the up position.

Ball Crunch

Stability Ball Ab Exercises

Place ball at low back area and place feet wide to stabilize the body. Cross arms over chest. In a controlled motion, keeping neck straight, curl upper body up. Contract abdominals fully without compromising form. While maintaining the controlled motion, return to starting position. Do not allow muscle to relax before next repetition. 

Ball Bicycle Intermediate

Stability Ball Ab Exercises

Primary Muscle Group: Core Muscles

Muscle groups worked in this exercise: Abdominus Rectus

Preparation: Lying on your back, bent your knees and place your feet on the floor. Hold the ball straight up above your chest. Bring both knees in toward your chest.

Ball Tummy Flattener

Stability Ball Ab Exercises

Primary Muscle Group: Abdominals

Muscle groups worked in this exercise: Abdominus Rectus, Internal and External Obliques and Transversalis.

Preparation: Lying on your back, place both heels on the ball with your knees slightly bent. Arms are at your sides.

Breathing: Exhale while lifting shoulders up; inhale as you lower back down to the floor.

Ball Side Flexion with Medicine Ball

Stability Ball Ab Exercises

Primary Muscle Group: Abdominal - Internal and External Obliques

Muscle Groups Worked in This Exercise: Side Abdominal - Internal and External Obliques, Deep Abdominal Muscles (transverse abdominis), and lower back (erector spinae)

Preparation: Lie on your side over the stability ball so your left hip is resting on the ball. Spread your legs for good solid balance.

Ball Pass

Stability Ball Ab Exercises

Primary Muscle Group: Abdominals

Preparation: Lie on your back on the floor with the ball between your ankles/calves and put your arms over your head.

Breathing: Inhale to grasp the ball, exhale after exercise.

Ball Natural Tummy Tuck

Stability Ball Ab Exercises

Primary Muscle Group: Core Muscles

Muscle groups worked in this exercise: Transverse Abdominus

Preparation: Begin in a pushup position, placing your shins on the ball and your hands position right under your chest on the floor. Tighten your abdominals and lift your hips so your back is flat.

Breathing: Exhale as you tuck your knees, Inhale when you return to start.

Ball Crunch Traditional

Stability Ball Ab Exercises

Primary Muscle Group: Core Muscles

Muscle groups worked in this exercise: Rectus Abdominus, Internal and External Obliques.

Preparation: Start by sitting on the ball with your knees bent and feet flat on the floor. Slowly walk your feet forward as you slide your torso down the ball. Your trunk should be parallel to the floor. Just let your hips clear the ball and let your lower back press into the ball; cross your arms over your chest.

Breathing: Exhale as you lift your torso, Inhale when returning to your start point.

Ball Crunch Intermediate

Stability Ball Ab Exercises

Primary Muscle Group: Core Muscles

Muscle groups worked in this exercise: Upper and Lower Abdominals

Preparation: Start by sitting on the ball with your knees bent and feet flat on the floor. Slowly walk your feet forward as you slide your torso down the ball. Your trunk should be parallel to the floor. Just let your hips clear the ball and let your lower back press into the ball; cross your arms over your chest.

Breathing: Exhale as you lift and inhale as you relax back to the starting point.

Ball Bottoms-Up Advanced

Stability Ball Ab Exercises

Primary Muscle Group: Quadriceps femoris, Gluteus, Abdominals

Muscle Groups Worked in This Exercise: Gluteus, Bicep Femoris

Preparation: Lie on the floor with your arms down at your sides, palms down. Only one heel and calf should rest on the top of the ball at a time.

Breathing: Exhale while you raise your hips, inhale when you release the position back to the floor.