Bangkok is a large city with severe Particulate Matter 2.5 (PM2.5) and traffic congestion problem. In past decades, traffic was the main cause of PM2.5. Due to the Covid-19 pandemic in 2020, Bangkok was in lockdown which substantially decreased traffic volume during that period. In this research, the author studied how this change in Bangkok’s traffic volume affected the concentration of pollution, especially PM2.5. Data were collected from 63 points in Bangkok and on 4 highways during January 2018 to December 2023. The analysis showed that during the lockdown period, the concentrations of PM2.5, NOX, NO2, NO and CO decreased by 14.38%, 12.93%, 18.43%, 2.65% and 5.66%, respectively, while traffic volume decreased by about 40%. However, there was no significant relationship between the concentration of PM2.5 and the decreased traffic volume. Therefore, the results indicated that while the Covid-19 pandemic might