Abstract: Objective: To investigate the clinicopathologic features, multi-differentiation, differential diagnosis and the prognosis of endometrial stromal tumors. Methods: The clinicopathologic data (including the histological characteristics, histochemical and immunohistochemical staining features), complication, differential diagnosis and the prognosis of endometrial stromal tumours were analyzed. Results: According to WHO Histological Typing of Female Genital Tract Tumours (2003), 50 cases with endometrial stromal tumors (ESTs) were divided into the endometrial stromal nodule (6 cases), (low grade) endometrial stromal sarcoma (30 cases), undifferentiated endometrial sarcoma (11 cases), mixed endometrial stromal and smooth muscle tumors (3 cases). Various tumors presented with multi-differentiation: 12 cases with smooth muscle, 10 with sex cord, 1 with fibrous, 1 with fibro-mucoid, and 1 with epithelial differentiation. In 10 cases, there were two types of differentiation. Moreover, 9 cases were associated with leiomyoma, in which 1 was case associated with adenomatoid tumor and 1 with well-differentiated endometrial adenocarcinoma. Conclusions: All types of endometrial stromal tumor can display multi-differentiation and associated with other type of tumor. They show various pathomorphological features. Among them smooth muscle and sex-cord differentiation are the most common types. Leiomyoma is the most commonly associated tumour. Histochemical and immunohistochemical stains can help diagnosis and differential diagnosis. Ten cases showed 30% positive rate for CD117, this may provide a theoretical basis for the molecular targeted-therapy to unresectable or mestastatic cases. There is no definite correlation between prognosis for the tumor and the types of multi-differentiation components of ESTs. But the invasion of tumor, the degree of atypical cell and the amount of nuclear mitotic figure all are a prerequisite for determination ofthe nature ofendometrial stromal tumors.