Dedifferentiated chondrosarcoma (CS) is a rare, highly malignant variant of CS in which a high-grade sarcoma coexists with a low-grade chondroid tumor. In this study, a novel dedifferentiated CS cell line, MS0812, was spontaneously established from mutated human embryonic muscle cells. Several features of the cell line were investigated, including growth characteristics, cytogenetics, electron microscopic features, expression of various antigenic markers and tumor formation. MS0812 has been cultured continuously for more than 3 years. The growth characteristics of MS0812 are similar to the immortalized cell lines as reported. The cell line exhibited complex karyotypes and hyperploidy, the chromosome number ranged from 50 to 158. MS0812 was positive for vimentin, desmin and muscle actin, indicating their muscle origin. With specific inductive condition, MS0812 differentiates into neural cells and adipocytes. Deletion of the p16 gene, which seemed to play a major role in the malignant phenotype of this cell line, was confirmed by PCR and immunocytochemistry. MS0812 formed tumors in nude mice, and the tumor revealed a fibrosarcoma with chondroid components, which were consistent with dedifferentiated CS as reported. Chondroid components showed metachromasia by Alcian blue and toluidine blue and were S100 and collagen-II positive. To our knowledge, this is the first report of the establishment of a human dedifferentiated chondrosarcoma from mutated human embryonic muscle cells, and it is a useful model for the study of the molecular pathogenesis of dedifferentiated CS.