The interaction between baicalin and human serum albumin（HSA） was investigated by fluorescence spectroscopy,circular dichroism,UV absorption spectroscopy,Fourier transform infrared spectroscopy and molecular modeling under simulated physiological conditions. The results indicated that the binding constants at 299 K and 309 K were calculated to be 1.28×105 L?mol-1 and 0.91×105 L?mol-1,respectively. The thermodynamic parameters（the enthalpy change（ΔH）：-26.2 kJ?mol-1；the entropy change（ΔS）：10.1 J?mol-1?K-1） suggested that electrostatic interaction was the predominant force in the baicalin-HSA complex,though there was hydrophobic interaction. Molecular modeling suggested that baicalin was located in subdomain ⅡA by hydrophobic and electrostatic forces,which agreed with the results obtained by fluorescence spectroscopy.The formation of the baicalin -HSA complex did not change the secondary structure of HSA by circular dichroism and Fourier transform infrared spectroscopy. Synchronous fluorescence showed that baicalin binding to HSA had changed the microenvironment around tryptophan（Trp）with polarity increasing.