Intensive monitoring for PM mass and composition was conducted during December 2006–February 2007 at a mixed site in Hanoi, Vietnam. Fluctuations in levels of 24 h PM2.5 (26–143 μg m−3) and PM10 (37–165 μg m−3) were examined in relation to weather conditions and regional synoptic patterns. High 24 h PM levels were observed at low wind speeds when a stagnating ridge governed over Northern Vietnam. Diurnal variations of PM mass and composition, analyzed using 4 h-samples, reflected the influence of local emissions with peaks of PM mass and EC/OC observed during morning and evening rush hours. The 24 h EC and OC levels in PM2.5, 1.5–4.9 μg m−3 and 10–39 μg m−3, respectively, constituted about 90% of the total EC and OC in PM10. Ionic species (SO4−−, NO3−, NH4+, Cl− and K+) were the major composition of PM2.5, whereas elements (Ca, Si, Al and Fe) were the major components in the coarse fraction (PM10–2.5). The reconstructed mass, explained 78 ± 11% of PM2.5 and 61 ± 11% of PM10–2.5, suggested significant contributions of secondary PM (OM,SO4−−, NO3− and NH4+) and combustion (biomass, diesel, etc.) to PM2.5. PMF model revealed 7 source factors of PM2.5: secondary mixed PM (40%), diesel traffic (10%), residential/commercial cooking (16%), secondary sulfate rich (16%), aged seasalt mixed (11%), industry/incinerator (6%), and construction/soil (1%). Contributions from local emission sources and the potential long-range transport were analyzed using the PM compositions and the diurnal variations in relation to local source activities, location of local sources, winds and air mass HYSPLIT trajectories. Major part of PM2.5 mass appeared to link to local emission origins. Additional measurement data are required to characterize the weekend–weekday and inter-seasonal patterns of PM.