Serum immunoglobulin (Ig) of Amur sturgeon Acipenser schrenckii, Chinese sturgeon, Acipenser sinesis and Huso sturgeon, Huso dauricus which were healthy and unimmuned, was first time respectively purified by using saturation ammonium sulfate precipitation followed by Sephadex G-200 gel column chromatography. Molecular weight and partial characterization of Ig and heavy chain and light chain of Ig were measured by polyacrylamide gel electrophoresis (PAGE), SDS polyacrylamide ge l electrophoresis (SDS-PAGE), Western blotting and Ouchterlony method. The results show that Ig molecular weight of Amur sturgeon, Chinese sturgeon and Huso sturgeon is 867 kD, 896 kD and 924 kD respectively. Heavy chain molecular weight of Ig in the three sturgeons' serum is all 88 kD and light chain of Amu r sturgeon and Chinese sturgeon is 29 kD, but there is an extra light chain of 26 kD in Huso sturgeon serum. The results of measurements and calculation show that Ig of sturgeon is tetramer. In Western blotting, Ig and Ig heavy chain of the sturgeons have the same antigenicity and can be detected by antibody of rabbit anti the sturgeon Ig respectively in colloxylin membrane while light chain cannot be detected. Serum and Ig in serum of the three sturgeons can react with serum of rabbit anti each of the three sturgeons' Ig, but cannot react with serum of rabbit anti Ig of carp Cyprynus carpio. The Ouchterlony results show that Ig of sturgeons are immune homologous in structure and sequence, but have little immune homologous characters compared with Ig of highclassification Osteichthyes such as carp.