A case of cesarean scar endometriosis with myxoid change and decidualization in a 24 year-old pregnant is presented. Patient in the second trimester complained of mass in the scar tissue of previous cesarean section. At 40th week of gestation, pregnancy was terminated and subcutaneous mass was removed. Microscopic examination revealed a lesion with lobular pattern and prominent myxoid change in the stroma. Each lobule was containing dilated cystic spaces resembling lymphatic vessels. Also signet-ring like vacuolated cells were present in myxoid stroma. The diagnosis was decidualized scar endometriosis with myxoid change. However, histological features of the lesion may cause diagnostic confusion with benign or malignant tumors such as myxoma, myxoid sarcomas and mucinous adenocarcinoma. Immunohistochemical study and thus recognizing cellular characteristics could help to prevent this misinterpretation.