Organic matter dynamics, structural change, and stable isotope ratio (¹²C/¹³C) were compared in O layer and A horizon (0-10 cm) in two temperate forests (secondary experimental deciduous forest of Kinki University and primary evergreen forest of Kasuga Taisha Shrine, Nara) in Japan and a tropical rainforest in West Sumatra, Indonesia. The O layer was stratified into Oi, Oe and Oa sub-layers, corresponding to undecomposed, intermediately decomposed and well decomposed or humified litter, respectively. In the deciduous forest, the range of the amount of carbon in litterfall for a period of one year was 2.5-5.5 t C/ha, with higher values on the upper slope than in the valley position. In the evergreen forest, the corresponding range was 2.5-3.6 t C/ha, with higher values on the upper slope than lower slope. In the Sumatra tropical rainforest, the corresponding range was 4.2-5.4 t C/ha. The carbon stocks in the entire O layer for a period of one year was 5.1-6.3 t/ha in the deciduous forests, 5.1-6.0 t/ha in the evergreen forests and 4.9-5.0 t/ha in the tropical rainforest. The range of the soil humic carbon stocks in the A horizon was 20-27 t/ha in deciduous forest, 63-81 t/ha in evergreen forest, and 13-16 t/ha in the tropical rainforest. The ¹³C NMR study showed that there was a structural change in soil humus content of the Oi, Oe, Oa layers and A horizon in the three forests. The ratio of aliphatic (0-40 ppm) and carboxyl (171-190 ppm) carbon tended to increase with increase in the amount of litter decomposed in the Oi to Oa layers and A horizon in the two temperate forests. We will discuss in details the mechanisms behind the differences in carbon stocks among the three forests examined.