Malignant change of endometriosis in a cesarean scar (CS) is rare. We report a case of carcinosarcoma arising from atypical endometriosis in a CS scar, which was successfully treated with complete excision of the lesion and repair of the abdominal wall defect with autologous skin-muscle flap graft. A 41-year-old woman presented with a recurrent endometriosis in a CS scar. Within 16 years it changed from benign to atypical endometriosis and finally to carcinosarcoma after three operations. Complete excision of the tumor was performed, with a big defect of abdominal wall successfully repaired by autologous pedicle skin-muscle graft. The diagnosis of carcinosarcoma arising from atypical endometriosis was confirmed histologically. The lesion recurred 6 months after the fourth operation. She died of disease 15 months after the fourth operation. This case demonstrated that long-standing recurrent scar endometriosis could undergo malignant changes and should be made aware. The primary treatment is complete surgical excision.