Many major cities in Southeast Asian countries suffer severe haze pollution due to rapid urbanization and motorization and biomass burning in forest and agricultural field. Our previous study of PM2.5 characterization in Bangkok demonstrated Organic Carbon Mass (OCM) accounted for 40% of total PM2.5. However, there are many unidentified sources of OCM, which becomes an obstacle for haze pollution mitigation. This study aims to assess PM2.5 source contributions using the data of organic markers and other components in PM2.5 collected at major cities of Southeast Asia. In the 1st year, intensive PM2.5 sampling will be implemented, and the unidentified organic markers, which are key compounds to identify specific sources of PM2.5, will be determined by Gas Chromatograph/Time-of-Flight Mass Spectrometer (GC/TOFMS). Then, the analytical conditions of the organic markers will be optimized. In the 2nd and 3rd year, daily PM2.5 sampling will be conducted during 2 weeks for each month, and the chemical components of PM2.5 such as ions, carbonaceous compounds, trace elements and organic markers will be analyzed. Regional and seasonal characteristics of the chemical components of PM2.5 will be clarified. Finally, PM2.5 source contributions is evaluated by the receptor models and the time profiles of the chemical components PM2.5. These results will provide scientific knowledge for PM2.5 pollution mitigation in Southeast Asian countries through outreach such as regional workshop.