AIM: To investigate the effectiveness of a modified inferior oblique muscle belly transposition for treatment of V-pattern exotropia combined with mild to moderate inferior oblique muscle overaction. METHODS: Thirteen cases (23 affected eyes) of V-pattern exotropia with inferior oblique muscle overaction (+ or ++) who underwent the modified inferior oblique muscle belly transposition procedure were retrospectively reviewed. The amount of V-pattern, grade of inferior oblique overaction, degree of vertical strabismus, abnormal head posture, and the fovea-disc angle were evaluated before and after surgery. RESULTS: The V-pattern was corrected in all cases, and the amount of V-pattern reduced by 17.85±5.13 prism diopter (PD) on average (t=16.07, P