Soot is effective to global warming by its strong light absorbance. The effect depends on its mixing state, that is, coated or non-coated by sulfate or other light-transparent materials. Japan is located west of China which is one of the strongest sources of anthropogenic aerosols such as soot, sulfate and organics. High loading of BC (black carbon) and sulfate frequently observed in Japan associated with long range transportation. However, mixing state of BC is not observed systematically. Aerosol samples were collected in Kanto plane (around Tokyo) and three mountain sites in central Japan (Mt. Haruna, Mt. Senjo and Mt. Hotaka) in different seasons during 2009- 2011. Morphologies of individual particles were observed using a TEM (transmission electron microscope) before and after irradiation of strong electron beams. In addition, modifications of particles at temperatures up to 500 °C were observed using refractory SiO substrate. Fine particles (< 1 ƒÝm) in winter and spring were dominated by sulfate. Considerable fractions of sulfate particles include soot. The number fraction of internally mixed soot varied from less than 5 % to near 100 %.