The interaction of BSA and NIC was investigated by absorption spectra, fluorescence spectroscopy and synchronous fluorescence spectroscopy. In the system of sodium phosphate dibasic-citric acid of 0.1 mol(-1) x L(-1), fluorescence titration showed that the fluorescence intensity of BSA at 342 nm was quenched when NIC was added, NIC was capable of binding with BSA to form a 1:1 complex and the quenching mechanism of BSA affected by NIC was shown to be a static quenching procedure by calculating the binding number n and binding constant K. NIC decreased the intensity of the characteristic absorption peak of BSA, showing that the binding of NIC to BSA had strong impact on protein conformation with the decrease in a-helical content of the protein. Synchronous fluorescence indicated that the binding of NIC to BSA is near tryptophan subunit.