Abstract: We examined the dynamics and community structure of soil mesomicroarthropods during litter decomposition in tropical rain forests of Xishuangbanna, SW China between May, 2000 and April, 2001.? The experiment was carried out in three plots of tropical seasonal rain forest located within a distance of 15 km. Mixed-species litterbags were constructed and placed in the field for one year. Soil meso-microarthropods were extracted from the litterbags by the Tullgren method each month during litter decomposition. The densities of soil meso-microarthropod groups and individuals were calculated per gram of dry litter (relative density). The data showed that Collembola and Acari were the most abundant groups of arthropods in the tropical seasonal rain forests (above 30%). Diversity indices, numbers of groups and number of individuals of soil meso-microarthropod were all higher in the middle stage of decomposition than in the early and end stages of decomposition. Variation of soil mesomicroarthropod communities, including abundance of some groups, was correlated with litter quantity and quality. Relative density of soil meso-microarthropod reflects the dynamic relationship between litter quality and number of groups and individuals of soil meso-microarthropods during the decomposition process. The differences of diversity and abundance of soil meso-microarthropods among three different plots were higher in the end stage of decomposition than ?in the early stage of decomposition, but litter weight loss did not differ among the three different study site plots.