This study aims to determine the in-vehicle and outdoor culturable airborne bacteria concentration, fine particle (PM2.5) concentration and particle number concentration for six size ranges (0.3-0.5 mu m, >0.5-1.0 mu m, >1.0-3.0 mu m, >3.0-5.0 mu m, >5.0-10 mu m, and >10 mu m) and to assess the relation between the culturable airborne bacteria and PM2.5 concentrations in different public transport vehicles. The measurement campaign was conducted in the morning and evening onboard of the Metrobus, red-bus and outdoors. PM2.5 concentrations in the Metrobus and red-bus were observed as 58.8 +/- 10.2 mu g/m(3) and 76.2 +/- 30.9 mu g/m(3), respectively, and the outdoor value was about two times more. For both types of public transportation, the amount of internal environment particulate matter and the amount of external environment particulate matter displayed a high level of correlation (red-bus/outdoors, R=0.97; Metrobus/outdoors, R=0.88) with the particulate matter size. The concentration of Staphylococcus aureus correlated with PM2.5 concentrations in the Metrobus and Staphylococcus spp. was found to be higher in in-vehicle. The number of commuters, vehicle ventilation type and outdoor air entering the vehicles probably caused the differences in in-vehicle culturable airborne bacteria and particle concentrations.