OBJECTIVE 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<0.001). The surgical cure rate for mild to moderate inferior oblique muscle overaction was 87.0% (20/23). The degree of the fovea-disc angle has a mean reduction of 5.45°±2.87° (t=3.95, P=0.003) after surgery. The mean vertical deviation in 5 cases with a small-angle hypertropia (5.23±3.06 PD) in the primary position reduced by 3.15±1.86 PD (t=6.10, P<0.001). No serious complications were observed. CONCLUSIONS The modified inferior oblique muscle belly transposition procedure can effectively treat mild to moderate inferior oblique overaction and relieve the V-pattern, which is safe and easy to perform.