To investigate the effect of oxygen radicals on the molecular properties of bovine serum albumin (BSA), the secondary and tertiary structures, molecular weight and optical anisotropy of BSA were examined after the irradiation of the protein at various doses. gamma-Irradiation of the protein solution caused the disruption of the ordered structure of protein molecules as well as degradation, cross-linking and aggregation of polypeptide chains. Fluorescence spectroscopy indicated that irradiation quenched the emission intensity excited at 280 nm. Fourier transform infrared spectroscopy (FTIR) indicated that irradiation caused transformation from beta-turns into beta-sheets. A light scattering study showed that increasing the radiation dose decreased the molecular weight of the protein. Optical anisotropy data showed that radiation changed the ordered structure of the protein. Ultraviolet absorption spectroscopy indicated that fragmentation and aggregation might occur in response to radiation exposure.