The interaction of mecobalamin and bovine serum albumin(BSA) was studied by fluorescence spectroscopy,ultraviolet absorption spectroscopy and resonance light scattering spectroscopy.The results showed that in pH 7.40 Tris-HCl buffer solution,both the fluorescence and resonance light scattering intensity were quenched when increasing the mecobalamin concentration.According to Stern-Volmer curve,the fluorescence quenching constant was calculated(Ksv=5.40×104,6.90×104,8.00×104 L/mol) with the interaction of mecobalamin and BSA at different temperatures(293,303,310 K).At the same time,ultraviolet absorption spectra were characterized.The experimental results indicated that the fluorescence quenching mechanism of mecobalamin with BSA was a dynamic quenching procedure.The binding constants(KA=1.68×104,4.34×104,7.90×104 L/mol),binding sites(n≈1) and the corresponding thermodynamic parameters,namely enthalpy change(ΔH),free energy change(ΔG) and entropy change(ΔS) at different temperatures were calculated(ΔH0,ΔG0,and ΔS0).According to the thermodynamic parameters,during the binding process,spontaneous molecular interaction occurs in which entropy increased and free energy decreased.These indicate the hydrophobic interaction was the main sort of binding force between the reaction of mecobalamin and BSA.In addition,the effect of mecobalamin on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy.The results revealed that mecoba-lamin did not change the conformation of BSA during the reaction.