In situ interaction of CdS nanorods (CdSNRs) with gelatin was investigated at pH 12.0. UV-Visible, FT-IR, scanning electron microscopy, dynamic light scattering, synchronous fluorescence, and three-dimensional fluorescence spectroscopy methods were used. It was found that negatively charged CdSNRs quenched the synchronous fluorescence of gelatin by forming a CdS/gelatin complex. The synchronous fluorescence quenching data were analyzed according to Scatchard equation, and the binding constants and corresponding thermodynamic parameters Delta H, Delta G, and Delta S at three different temperatures were calculated. Small positive enthalpy (Delta H) and entropy (Delta S) values indicate that both electrostatic and hydrophobic forces played the major roles in the binding reaction of CdSNRs with gelatin. The effect of CdSNRs on the conformation of gelatin was also analyzed from both synchronous fluorescence and three-dimensional fluorescence spectra. The results provide useful information for exploring the chemical mechanism of interaction between nanomaterials and fibrous protein. (C) 2011 Elsevier Inc. All rights reserved.