Abstract?AlM: To study the number of myogenin - positive activated satellite cells in the inferior oblique muscles and the medial muscles of V- pattern exotropia with inferior oblique overaction, to further explore the possible etiological factors of V-pattern exotropia with inferior oblique overaction.? METHODS: The inferior oblique muscles and the medial muscles were cut from V - pattern exotropia patients with inferior oblique overaction during strabismus operation treated as the strabismus group. Cross sections were stained immunohistochemically for the presence of activated satellite cells, as identified by myogenin immunoreactivity. The inferior oblique muscles and the medial muscles were obtained from the corneal transplant donors ( six eyes of six cases) , which treated as the control group.? RESULTS: The frequency of myogenin - positive satellite cells of the inferior oblique muscles was (22. 7± 7.03)% and (4. 2±0. 75)% in the strabismus group and the control group. Significant differences existed in the expression of myogenin in two groups (P<0. 05). Again, the frequency of myogenin-positive satellite cells of the medial muscles was (2. 2±0. 75)% and (4. 5±1. 05)% in the strabismus group and the control group. Significant differences also existed in the expression of myogenin in two groups (P<0. 05).?CONCLUSlON: lt is first report that myogenin-positive satellite cells presents in extraocular muscles of V -pattern exotropia with inferior oblique overaction. The current results suggest that myogenin is one of possible etiological factors of V-pattern exotropia with inferior oblique overaction.