The objective of this study is assessment the risk of microorganism (total bacteria and totalfungi) in lecture room indoor air of Srinakharinwirot University Ongkaruk. The sampling ofmicroorganism in indoor air was gathered at difference sampling areas and any comfort environmentalfactors for the risk characterization descriptive in microorganism exposure.From results, the average of total bacteria and total fungi in lecture room indoor air was 398.3and874.0 CFU/m3 respectively. The comfort environmental factors in almost lecture room were notcomfortable for user. The air conditional system may be source of bacteria, but not be source of fungithat it may come from others source such as ceiling or walls. Thus, at ¼ distance from air conditionalvent to opposite wall position is the significant highest of microorganism exposure risk (p = .050). Onthe others hand, the fungi exposure at any distance from air conditional vent is not significant.Thus, the improvement of lecture rooms are be need. They will be improved for both of factorstogether; agent (microorganism) and environment (comfort environmental factors). The efficiencyventilation will significant decreased the bacteria exposure risk (p = .012), and the efficiencyenvironmental
