Abstract: The binding reaction of the drug,paracetanol (PTL),with bovine serum albumin (BSA) was studied by fluorescence spectrophotometry and UV-VIS spectrophotometry,in simulating physiological environment of human body.It was found that the fluorescence intensity of BSA was remarkably reduced due to fluorescence quenching through non-radiative energy transfer.Experimental data were treated by the stern-Volmer equation and the Lineweaver-Burk equation,and the static equilibrium constant (KLB) of the binding reaction was found to be 2.592×103mol·L-1 (297 K),and the binding locality was 1.94 nm apart from the 212 sited tryptophan.According to the thermodynamic parameters of the reaction,the binding power was primarily the force due to hydrophobic action.