Polylactic acid (PLA) is one of the most popular biodegradable plastics favored over traditional plastics. However, it is more difficult to degrade than other biodegradable plastics probably due to the low species and number of PLA-degrading microorganisms degrading enzymes in the environment. Therefore, identifying PLA-degrading microorganisms and enzymes is of great significance for the popularization and application of PLA. This study identified a PLA-degrading enzyme, S8 serine peptidase (S8SP), from Bacillus safensis, and the heterologous expression of S8SP was conducted in Escherichia coli. PLA degradation ability of S8SP was investigated using scanning electron microscopy and water contact angle. The surface of S8SP-degraded PLA films showed obvious cracks and pits and exhibited improved hydrophilicity. The molecular weight of S8SP was about 42 kDa, and its optimum temperature and pH were 40 °C and 8.0, respectively. S8SP could maintain high stability in the temperature range of 30-40 °C and pH range of 7.0-9.0. Sodium ions (Na+), potassium ions (K+), Triton X-100, and Tween-80 promoted the enzyme activity of S8SP. S8SP had a high similarity degree to S8 serine peptidase from the genus Bacillus, and had the classical hydrolase-catalyzed triplet structure.