OBJECTIVES: Microplastics have been detected in the atmosphere, raising concerns about their impact on the lungs. There have been reports on the effects of surface functional groups in evaluating the physicochemical properties of microplastics, but no reports have evaluated their chronic effects. We performed intratracheal instillation in rats to evaluate the acute and chronic effects on the lungs of microplastics with different surface functional groups. METHODS: Unmodified, NH2-modified, and COOH-modified polystyrene particles with a particle size of 1 μm were intratracheally instilled into the lungs of rats. Rats were dissected at 3 days, 1 week, 1 month, 3 months, and 6 months after exposure to analyze inflammatory cells and lung injury factors in bronchoalveolar lavage fluid (BALF) and to observe histopathological findings in the lungs. RESULTS: A significant increase in the number of inflammatory cells in BALF was observed up to 1 week after exposure to the NH2-based modified polystyrene compared with the negative control group. A significant increase was observed 3 days after exposure, and histopathological findings in the lungs also showed an influx of inflammatory cells into the alveolar space in the acute phase, but not in the chronic phase. In in vitro studies using RAW cell lines, NH2-based modified polystyrene also induced the highest oxidative stress compared with unmodified and COOH-based modified polystyrene. CONCLUSIONS: These results suggest that these polystyrenes do not have high pulmonary toxicity, although there are differences in toxicity due to differences in surface functional groups only in the acute phase.