AbstractThe binding of isofraxidin to bovine serum albumin (BSA) was studied under physiological conditions with BSA concentration of 1.5×10−6 mol · L−1 and drug concentration in the range of 1.67×10−6 mol · L−1 to 2.0×10−5 mol · L−1. Fluorescence quenching spectra in combination with uv absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and CD spectroscopy was used to determine the drug‐binding mode, binding constant, and the protein structure changes in the presence of isofraxidin in aqueous solution. The linearity of Scatchard plot indicates that isofraxidin binds to a single class of binding sites on BSA and the values given for the binding constants agree very closely with those obtained by the modified Stern‐Volmer equation. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS), were calculated to be −17.63 kJ · mol−1 and 51.38 J · mol−1 · K−1 according to the van't Hoff equation, which indicated that hydrophobic interaction played a main role in the binding of isofraxidin to BSA. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004