Background <p>Research on combined effects between ambient particulate matters (PMs) and Folate (FA) with respect to cognitive function remains limited. This study aimed to investigate whether long-term PMs exposure could modulate the association between FA and cognitive function in Chinese older adults.</p> Methods <p>The study was composed of 3,880 individuals aged 60 and above. The cognition of the subjects was assessed using the Montreal Cognitive Assessment - Basic Version (MoCA-B). Folate concentration was measured through laboratory serum analysis, and data on ambient particulate matter levels were acquired from the China High Air Pollutant (CHAP) monitoring network. A linear regression analysis was conducted to explore how FA and PMs interact to affect cognitive function, with stratified analysis based on thresholds identified using restricted cubic splines (RCS).</p> Results <p>Based on the results of the linear trend analysis, PMs exposure exhibited a negative with MoCA-B scores (all <i>P</i>_trend &lt; 0.001); RCS analysis further revealed that the exposure-response relationships for PM_2.5, PM₁₀ and MoCA-B scores exhibited significant non-linear characteristics (<i>P</i> &lt; 0.05), identifying their effect inflection points. FA was positively associated with MoCA-B scores (<i>β</i> = 0.107, 95% <i>CI</i>: -0.073, 0.287), and this association was effect by PM_2.5 and PM₁₀ exposure levels: as their concentration increased, the positive association was attenuated; When the exposure concentration exceeded 64.54&#xa0;µg/m³and 103.9&#xa0;µg/m³, the association even replaced by a negative association.</p> Conclusion <p>Our findings indicated that PM exposure were associated with an attenuated positive association between FA and cognitive function, and even a negative association.Therefore, further action must be taken to reduce the harm caused by air pollution to enhance the cognitive benefits of FA.</p>