Among various nanomaterials used for food packaging, zinc oxide (ZnO) nanoparticles are one of the best choices due to their high antimicrobial property. However, for biodegradable materials like poly(butylene adipate-co-terephthalate) (PBAT), biodegradability can be limited by the antibacterial function. Thus, in the present study, reinforced PBAT films with different weight percentages (1, 3, and 5 wt%) of ZnO nanoparticles were prepared by the casting process to investigate the effects of ZnO on the thermostability, mechanical, and antimicrobial properties of the PBAT film. The results showed that the small amount of ZnO (1 wt%) reduced the decomposition temperature of the PBAT film by nearly 50 °C, and the thermal stability was significantly decreased with the increasing ZnO content. Melt flow index comparison showed that the ZnO nanoparticles accelerated the room temperature degradation rate of PBAT films. In addition, due to the degradation effect of ZnO nanoparticles, the mechanical properties such as the total percentage of elongation (at break), the tensile strength, and yield strength decreased with the addition of ZnO nanoparticles. The antibacterial test showed that PBAT + 1 wt% ZnO films could achieve high antibacterial activity ( R = 6.8) against Escherichia coli . This study is important for controlling the degradation period of biodegradable materials.