Objective To observe the changes in the expression of nerve growth factor （NGF） and myocyte differentiation factor 5（Myf5） in the medial rectus muscle of a cat model with strabismus. Methods Eighteen cats that were in the 4-6 weeks sensitive period were selected for surgery to create an exotropia model. All animals were randomly divided into experimental and control groups. Medial rectus muscles from both the experimental and control groups were collected at 1 month， 2 months， and 3 months after strabismus surgery. These samples were prepared for histologic examination by fixation， paraffin embedding and slicing. Immunohistochemistry staining was used to detect NGF and Myf5 expression and an optical density analysis was used to measure the average optical density. Data were analyzed using t test or t′ test， repeat measured ANOVA and Pearson correlation test. Results ①There were significant differences in NGF expression in the medial rectus muscles of the experimental and control groups between 2 and 3 months （t=7.678， 15.532， P＜0.01）. ②There were also significant differences in the expression of Myf5 in the medial rectus muscles of the experimental and control groups between 2 and 3 months （t=5.819， 7.029， P＜0.01）. ③There was a negative relationship between NGF and Myf5 expression and the development of strabismus （r=-0.984， -0.971， P＜0.05）. Conclusion ①The surgical method can successfully produce a concomitant exotropia cat model. ②The reduced expression of NGF and Myf5 in the medial rectus muscle in the experimental strabismus cat model may be involved in the occurrence of strabismus. ③NGF and Myf5 expression in the medial rectus muscle are reduced with the duration of the extension， which may be related to the progress of a strabismus condition.