Objective Particulate matter 2. 5 (PM2. 5) is an important source of air pollution and can cause respiratory and other systemic diseases. Additionally, PM2. 5 can cause cognitive decline, though the exact mechanism is not clear. This study aimed to explore the mechanism by which exposure to environmental PM2. 5 via air pollution induces cognitive impairment. Methods This study used the PM2. 5 online collection and exposure system on C57BL/ 6 mice to make a PM2. 5 exposure mouse model. Mice were exposed for 4 h per day, 5 days per week, for 15 weeks. After the model was established, mouse behavioral symptoms, pathological features and related molecular mechanisms were examined in each group. Results PM2. 5 exposure result ed in pathological changes in lung tissue in mice and exacerbated their cognitive impairment. Immunohistochemical staining of the central nervous system detected microglial cell activation. The level of IL-6 also increased in the central nervous system of exposed mice compared with control mice. PM2. 5 exposure did not cause damage to other major organs in the mice. Conclusions The result suggest that PM2. 5 induced neuroinflammation and promoted the activation of microglial cells in the hippocampus, thus aggravating cognitive impairment in mice.