Abstract: An osteosarcoma associated antigen (OSAA) was partially purified from human osteosarcoma tissue by means of hypertonic potassium chloride extract and immunoaffinity chromatogrphy. The OSAA was demonstrated as a glycoprotein with a molecular weight of 57 KD by the analyses of sodium dodecyl sulfate polyacylamide gel electrophoresis, westen blotting and periodic .acid-schiff reagent staining, and called it Ogp57. Following the antigen assay and comparing with the known related antigens, we suggest the Ogp57 may be a novel OSAA.