<p>Long-term exposure to particulate matter (PM2.5) primarily affects the respiratory and cardiovascular systems, resulting in millions of premature deaths per year. However, the influence of PM2.5 risk perception on health decisions and preventive behaviors remains a research gap. Thus, this study examined such risk perception and associated sociodemographic factors in urban Thailand. For this purpose, a cross-sectional survey of 921 participants was conducted from March–May 2024 in urban Bangkok and Chiang Mai, Thailand. PM2.5 risk perception (13-item scale) was measured as self- administered the online survey. Binary logistic regression was also employed to test the association between sociodemographic factors and PM2.5 risk perception as well as the association between risk perception and preventive behaviors. Based on the findings, the majority of the participants agreed on their susceptibility to and the severity of PM2.5, while the sociodemographic factors showed that in urban Chiang Mai, females with higher education and income, who obtained information from various news channels, were more likely influenced by their PM2.5 risk perceptions. Regarding their PM2.5 preventive behaviors, the participants reported staying indoors, limiting outdoor activities, using air purifiers, and wearing N95 masks. The implication of the findings is that more education and information campaigns should be implemented to drive policies, raise awareness, and eliminate PM2.5-specific dust pollution sources.</p>