Diosgenin (DIO) is the active ingredient of Dioscorea species. The interaction of DIO with bovine serum albumin (BSA) was investigated through spectroscopic methods under simulated physiological conditions. The fluorescence quenching data revealed that the binding of DIO to BSA without or with Co(2+) or Zn(2+) was a static quenching process. The presence of Co(2+) or Zn(2+) both increased the static quenching constants K SV and the binding affinity for the BSA-DIO system. In the sight of the competitive experiment and the negative values of ΔH (0) and ΔS (0), DIO bound to site I of BSA mainly through the hydrogen bond and Van der Waals' force. In addition, the conformational changes of BSA were studied by Raman spectra, which revealed that the secondary structure of BSA and microenvironment of the aromatic residues were changed by DIO. The Raman spectra analysis indicated that the changes of conformations, disulfide bridges, and the microenvironment of Tyr, Trp residues of BSA induced by DIO with Co(2+) or Zn(2+) were different from that without Co(2+) or Zn(2+).