Abstract: Objective: To explore the expression of signal transducer and activator of transcription 3(STAT3) in osteosarcoma and its relationship with tumor microvascular density(MVD) . Methods: The STAT3 expression of 47 cases with osteosarcoma were detected by immunohistochemistry. The clinical data，pathological classification and clinical index of 47 cases were compared. MVD of osteosarcoma was counted. The correlation between the expression of STAT3 and MVD was analyzed. results: The exprssion of STAT3 was mainly in the cytoplasm. The expression levels of STAT3 in osteosarcoma were significantly higher than that in normal bone tissue(P ＜ 0. 01) . The expression levels of STAT3 in osteosarcoma with stage Ⅱa，Ⅱb and Ⅲ were significantly higher than those in stage Ⅰ(P ＜ 0. 01) , the expression of stage Ⅲ was significantly higher than stage Ⅱa and Ⅱb(P ＜ 0. 01) . The expression levels of STAT3 in invasive soft tissue were significantly higher than that in no-invasive soft tissue(P ＜ 0. 01) . The expression of STAT3 in osteosarcoma was positively correlated with MVD(P ＜ 0. 05) . Conclusions: The expression of STAT3 in osteosarcoma is correlated with tumor clinical stage and soft tissue invasion, and its expression is positively correlated with MVD. The high expression of STAT3 may play an important role in the development of osteosarcoma, and which is closely correlated to the angiogenesis of osteosarcoma.