Abstract: The photo-oxidation of PBS and PBS/ZnO nanocomposites with different ZnO loadings were studied in this paper. The PBS/ZnO nanocomposites were prepared by melt-compounding process and the ZnO dispersion state within the PBS matrix was analyzed by TEM. The reduction of molecular weight of PBS nanocomposites was lower than that of the neat PBS, which indicates more chain scission happened in neat PBS. The chemical structure changes characterized by FTIR and PGC-MS showed that ZnO nanoparticles can stabilize the PBS matrix and possible molecular structure of degradation products were given. Carbonyl index and hydroxyl index of PBS grew more significantly than PBS nanocomposites. Much more degradation products accumulated in PBS samples than in the PBS nanocomposite samples. Thermal properties analyzed by DSC revealed a decrease of crystallization temperature in all samples, which is due to the formation of short chains after irradiation. In addition, the small fragments could recrystallize and increase the crystallinity. SEM images of sample surfaces revealed that PBS sample had severer damages on surface than PBS/ZnO nanocomposites. These results demonstrate that ZnO nanoparticles can hinder the photo-oxidation of PBS. Keywords: biodegradable, poly(butylene succinate), ZnO, nanocomposites, photooxidation