Carbon fixation by soil is considered to be effective in controlling global warming. Since 40% of Japan's agriculture and forestry is in hilly and mountainous areas, hilly and mountainous soils have the potential to sequester carbon from the atmosphere. However, there is little knowledge about the actual condition of soil carbon content in hilly and mountainous areas and its variation factors. Therefore, we investigated the variation factors of soil carbon content in the intermountainous areas of the Kanto and northern Kyushu regions. We also examined the effects of soil application of charcoal and bamboo charcoal. Soil carbon content was affected by the soil carbon content before test (R=+0.99), average air temperature (R=-0.54), and soil exchangeable CaO content (R=+0.59). No changes in soil carbon content due to the application of charcoal or bamboo charcoal were observed at all test sites in this research.