Endometriosis of a surgical scar is rare and occurs mainly when a hysterectomy or Cesarean section was performed. We describe a 54-year-old woman with a large suprapubic mass as a definite case of a endomerioid carcinoma developing within the scar endometriosis following Cesarean section. Scar endometriosis, as well as endometriosis at other sites, can turn malignant. Endometrioid carcinoma is the most common histological pattern of malignant tumor arising in endometriosis. But clear cell carcinoma is very unusual. A case of primary clear cell carcinoma in endometriosis of a Cesarean section scar is described. To the best of our knowledge, this is the first documented case of endomerioid carcinoma developing within the scar endometriosis in Korea.