The goal of this study was to determine the impact of the COVID-19 partial lockdown on air pollutants in Hanoi, Vietnam. Concentration samples of PM2.5, nitrogen dioxide (NO2), ozone (O3), and sulfur dioxide (SO2) were taken from three sites. Results reveal that NO2 concentrations decreased from 21.6 μg/m3 to 5.2 μg/m3 (75.8% decrease), SO2 declined 60.7%, PM2.5 decreased by 55.9% with an absolute decrease of 55.0 μg/m3, O3 decreased by 21.4%, and average concentrations of PM2.5 were lower than ambient air quality standards during the partial lockdown. Authors suggest that the decline in air pollutants was attributed to a decrease in emissions from cars and shut down of industries during COVID-19.