Inhalable particulates, including PM10 and PM2.5, were collected on the campus of China University of Mining and Technology during the Summer Olympic Games of Beijing in 2008. The mass concentrations of PM10 and PM2.5 were monitored. The morphology and size distribution of individual particles in PM10 and PM2.5 were investigated by a high-resolution Field Emission Scanning Electron Microscopy (FESEM) and image analysis (IA). The toxicity reflected by bioreactivity of PM10 during the Olympic Games was also studied by Plasmid DNA assay. The results showed that the mass levels of PM10 and PM2.5 were well below 81.6 microg x m(-3) and 54.6 microg x m(-3), meeting the second ambient air quality standard of China. The ratio of PM2.5 and PM10 was averaged 0.63, indicating that the PM10 is dominated by fine particles. In terms of microscopic morphology, four types of particles were identified, including spherical particles, soot aggregates, minerals and unresolved fine particles, with the spherical particles and unresolved particles being the predominant components. Most PM10 and PM2.5 particles were in the size range of 0.1-0.4 microm, displaying a unimodal pattern. Volume-size distribution of PM10 exhibited a bimodal pattern with the peaks in 0.4-0.5 pm and 1-2.5 microm, and PM2.5 particles were mainly concentrated in the range of 1-2.5 microm. The results from plasmid assay showed that the bioreactivity of PM10 during the Olympic games was obviously lower than those of past summers, with the TD20 (toxic dosage of PM10 causing 20% plasmid DNA damage) being higher than those of the past summers.