Abstract: The degradation properties of poly(propylene carbonate) (PPC)/poly(lactic acid)(PLA) blends were studied under natural light irradiation, andthevariations in mechanical properties, weight loss, surface microstructure of the blends were investigated.The results indicated that the weight-loss rate of the blends were 34.89 wt%，40.50 wt%，39.38 wt%，29.6 wt% and 6.24 wt% at the PPC/PLA mass ratios of 100/0, 70/30, 50/50, 30/70 and 0/100, respectively, after irradiation for 56 days. The blends lost almost all of their mechanical properties after irradiation for 14 days. There were obvious cracks and holes found on the surface of pure PPC and PPC/PLA blends at a mass ratio of 50/50 after irradiation for 56 days, and however there was no change found on the surface of pure PLA.It was also observed that the longer the irradiation time, the coarser the surface of blends, and the greater was the degree of degradation. The hydroxyl index and carbonyl index of the blends were found to increase continuously at the first 21 days, especially within the first 14 days.The relative molecular weight and polydispersityindex of the blends decreased, which made the molecular weight distribution narrowed after irradiated for 56 days accordingly. Moreover, the blends presented an increase in thermal decomposition temperature and weight loss temperature (Tp) at a maximum rate, whereaspure PPC showed a decrease in TP after irradiation.