Abstract: Objective To discuss the clinicopathologic characteristics, immunophenotype, pathologic diagnosis and differential diagnosis of extraskeletal osteosarcoma (EOS). Methods We collected extraskeletal osteosarcoma samples from 4 EOS patients and observed the patients clinic characteristics, pathologic histology and immunophenotype, and then review the correlative literatures. Results The 4 patients are all male with an average age of 35.5 years old. They represented with soft lump without pain or tenderness. Three tumors located in low limbs, and 1 case in upper limbs. Two cases are myofibroblastic EOS, 1 case is small cell type and the other case is MHF-like type. Pathology examination: (1)Grossly, the 4 tumors'average maximum diameter is 4 cm. Section shows gray, soft and crisp, and the boundary are clear. (2)Histologically, the myofibroblastic type presents lobular frame, and the tumor cells are spindle or oval. Small cell type shows diffuse identical cells. MHF-like type appear with pleomorphic cells companion multinucleated tumor giant cells. (3)Immunohistochemistry: The 4 cases tumor cells all express VIM(4/4), OC(4/4), and 1 case expresses OCT(1/4). S100, desmin, CD34, NSE and SMA are all negative in the 4 cases. Conclusions Extraskeletal osteosarcoma is a kind of rare soft issue tumor, and the mainly diagnosis evidence is the specific pathologic characteristics, and immunohistochemistry can assist diagnosis and differentiate diagnosis.