Abstract:As a preliminary contribution to the systematic study on the ecology of viable soil seed banks under different tropical forests in Xishuangbanna, the present paper examines the store and dominants of viable seeds in the soils of 10 cm depth in a seasonal rain forest charactered by Pometia tomentosa, Term inalia myriocarpo and three secondary forests respectively dominated by Macaranga denticulata, Trema orientalis and Mallotus peniculatus. The results display that Macaranga denticulata forest and Trema orientalis forest have the most abundant soil seed banks with the seed densities of 29 945 ±2 267 seeds / m2 and 24 740 ±2 275 seeds / m2(mean ±SE, n = 20), respectively. The seed density in the soil of seasonal rain forest is 5 905 ±202 seeds / m2,and Mallotus peniculatus forest is only 3 345 ±438 seeds / m2. Herb is the most dominant propor-tion in the composition of soil seed banks of these four forest types, which, however, is decreased as forest becomes older in the secondary succession.