Concentration of particulate matter (PM) in Bangkok Metropolitan Region (BMR) is normally higher than the ambient air quality standard of Thailand, especially during winter. However, the linkage between PM and human health in this area is underreported. This study aimed to investigate the relationship between PM and outpatient department (OPD) visits for respiratory diseases among children aged 0–14 years in BMR. OPD visit data were obtained from the National Health Security Office from January, 2015 to December, 2018. Air pollution data, including particulate matter with aerometric diameter up to 2.5 μm (PM 2.5 ) and 10 μm (PM 10 ), as well as meteorological data were obtained from the Pollution Control Department during the same period. Two-stage approach was used to investigate the association between PM and OPD for respiratory disease among children in BMR. In the first stage, time-stratified case-crossover design with conditional logistic regression model was used to examine province-specific estimate. In the second stage, the province-specific estimate was pooled to derive BMR estimate using random-effect meta-analysis through maximum likelihood estimation. Odds ratio of respiratory OPD among children in BMR per 10 µg/m 3 increase in PM 10 and PM 2.5 was 1.0256 (95% CI: 1.0160, 1.0325) and 1.0338 (95% CI: 1.0091, 1.0585), respectively. This finding suggests that an increase of PM 10 and PM 2.5 was associated with increased risk of OPD for respiratory disease among children in BMR. Therefore, local government should develop and improve the existing air pollution control strategies to reduce PM concentration.