This study conducted roadside particulate sampling to measure the total suspended particulate (TSP), PM10 (particles <10μm in aerodynamic diameter) and PM2.5 (particles <2.5μm in aerodynamic diameter) mass concentration in 11 urbanized and densely populated districts in Hong Kong. One hundred and thirty-three samples were obtained to measure the mass concentrations of TSP, PM10 and PM2.5. According to these results, the TSP, PM10 and PM2.5 mass concentrations varied from 94.85 to 301.63μgm−3, 67.67 to 142.68μgm−3 and 50.01 to 125.12μgm−3, respectively. The PM2.5/PM10 ratio of all samples was 0.82 which ranged from 0.62 to 0.95. The PM levels and PM ratios in metropolitan Hong Kong significantly fluctuated from site-to-site and over time. The PM2.5 mass concentration in different districts corresponding to urban industrial, new town, urban residential and urban commercial were 77.64, 87.50, 106.96 and 88.54μgm−3, respectively. The PM2.5 level is high in Hong Kong, and for individual sampling, more than 60% daily measurements exceeded the NAAQS. The mass fraction of PM2.5 in PM10 and TSP is relatively high when compared with overseas studies.