Abstract: AimTo study the binding of sibutramine hydrochloride (SH) and bovine serum albumin (BSA) in physiological condition by spectroscopic method. MethodsThe quenching mechanism of the fluorescence of bovine serum albumin by sibutramine hydrochloride was studied with the fluorescence and the absorption spectroscopy. The binding constants K and the number of binding sites were determined at different temperatures according to Scatchard equation and the main binding force was discussed by thermodynamic equations. The effect of the drug on bovine serum albumin conformation was also studied by using synchronous fluorescence spectroscopy. ResultsThe quenching mechanism of sibutramine hydrochloride to bovine serum albumin was static quenching. The binding constants K at 8 ℃, 25 ℃, 37 ℃ were 1.21×10⁵, 8.31×10⁴, 6.97×10⁴ L·mol^-1 with one binding site, respectively. The thermodynamic parameters of the reaction were ΔH=-9.70 kJ·mol^-1, ΔS=56.41 J·mol^-1·K^-1. ConclusionThe binding force is electrostatic interaction. Sibutramine hydrochloride can be deposited and transported by serum protein in vivo. Sibutramine hydrochloride has nearly no effect on the serum protein conformation.