As a result of their biodegradability and biocompatibility, various nanoparticles using poly(lactic-co-glycolic acid) (PLGA) as a copolymer have shown promising results in biomedical engineering fields, including molecular imaging and drug delivery. However, the potential nanotoxicity of PLGA-based nanoparticles in the environment was poorly understood. Measurement of bacterial nitrification activities and changes in the soil microbial community are both critical parameters that should be used to evaluate potential distrurbances in the functioning of the environmental ecosystem. This study aimed to investigate the impact of PLGA nanoparticles with different zeta-potentials on nitrifying bacterial communities in the soil environment. In pure culture studies, the ammonia oxidation was inhibited by higher than 50% when PLGA cocentration is more than 0.05 mg/L or more regardless of zeta potential and exposure time, but the negligible effects were observed on the nitrite oxidation by most conditions. In the soil microcosm experiment, at the 0.05 concentration of the oparticles, the ammonia and nitrite oxidation were inhibited by more than 50% on the first day regardless of the nanoparticle composition, but all the activity was recovered after 14 days. These results provide a fundamental information on the toxcity of PLGA nanparticles on ecologcial function.