To better understand the mechanism of drug binding to proteins, the binding properties of taurine and its derivative 2-phthalimido-ethanesulfonic acid (PESA) with human serum albumin (HSA) were investigated under physiological conditions by calorimetry, circular dichroism (CD) spectroscopy and molecular modeling. Based on the thermodynamic data, molar reaction enthalpy, reaction order (n) and the rate constant (k) were calculated, the kinetics equations of TAU and PESA binding to HSA were obtained; hydrogen bond force played a major role in the complexes; the reactions were spontaneous; binding sites of both complexes were one site. The results of CD spectroscopy showed that the conformation of HSA−TAU and HSA−PESA did not have any high-ordered structural change. Computational mapping revealed the details of their binding conformations.