Abstract: The binding of Cd2+ to human serum albumin (HSA) is studied by gel chromatographic method with a radioactive indicator 115mCd. A new buifer system consisting of boric acid, sodium borate and glycerol is used. In the whole concentration ranges of free Cd2+ (7.24× 10-4-2.54×10-3M) only mononuclear binding species are detected at pH=7.28±0.04, μ=0.1and t=25℃. The average number of Cd2+ bound by a HSA molecule, ZB, as a function of free Cd2+ concentrations b is found to be ZB(b)= 14.0876+ 1.1360 lnb +1.43296. The number of binding sites of HSA towards Cd(Ⅱ) is 14 with an intrinsic equilibrium constant, 1.25×103.