Purpose: To report a pair of monozygotic twins with phenotype of fixating eye and strabismus having presented mirror image. Case : We report a case of five-year-old monozygotic twin sisters with strabismus. The elder sister's fixating eye was left, and the younger sister's fixating eye right. Both sisters were diagnosed with exotropia and the alternating prism cover test examination showed the elder sister with distant vision 18 ΔXT and near vision 28ΔX(T), and the younger sister with distant vision 18ΔXT and near vision 28 ΔX(T). We performed 4-mm resection of the rectus muscle and 4-mm recession of the external rectus muscle on the non-fixating eye for both sisters. Orthophoria on distant vision was obtained in both sisters after surgery. Conclusion : The phenotype of the strabismus presented a mirror image in monozygotic twins, and participation of an inherited factor was suggested in the appearance of strabismus.