In this study, organic marker compounds in fine particulate matter（PM_2.5）were observed during four seasons at forested（Akagi）, suburban（Maebashi）and urban（Saitama）sites in the Kanto region of Japan, and the source contributions of PM_2.5 were evaluated. Organic compounds were analyzed using an extraction-derivatization GC/MS method. PM_2.5 samples were also analyzed for ion components, organic carbon, elemental carbon and metallic elements. At both urban and suburban sites, the concentrations of levoglucosan（a biomass burning marker） increased in winter and fall, whereas dicarboxylic acids （photo oxidation products） increased during warm seasons. At the forested site, the concentration of 2-methyltetrols（a biogenic secondary organic aerosol（BSOA）marker from isoprene） tended to increase during warm seasons, especially in summer. The levels of organic markers for cooking and vehicle emissions were higher at the urban site than the other sites. As a result of positive matrix factorization analysis using a PM_2.5 component data set, it was possible to apportion 80-90％ of PM_2.5 mass concentration to 12 sources, including sources of organic particles such as biogenic primary/secondary origin, biomass burning and cooking. The contribution ratios of these sources involved in organic aerosols in PM_2.5 were estimated to be 41％at the urban, 39％ at the suburban, and 46％ at the forested site. These results will provide basic data for planning of future PM_2.5 reduction measures in Japan.