Abstract: To investigate the characteristics of soil fauna community structure in forest-steppe ecotone on Southeastern Inner Mongolia Plateau, the soil fauna communities from 4 different vegetation zones were investigated. A total of 53 722 soil fauna were collected and classified into 6 phyla, 11 classes, and 27 orders, respectively. The dominant groups were Coleoptera, Stylommatophora, Microdrile oligochaetes, Collembola and Hymenoptera among macro-soil-fauna; whereas the dominant groups were Collembola and Acarina among soil meso-and micro-fauna; and the dominant group was Rhabditidia among soil animals of wet type. The individual numbers and the group numbers were declining with the transition from the forest zone to the steppe zone, among which forest zone and forest-meadow area had the highest number of groups as well as the meadow-steppe area in the ecotone and forest zone had the highest number of individuals. Besides, there are differences in numbers and compositions of the dominant groups of soil animal in different vegetation zones and significant difference especially in density-group index (DG), Pielou evenness index (J) and Simpson dominance index (C). The individual numbers and group numbers of soil animals in different vegetation zones showed clear surface assembly. The maximum of the group numbers appeared in summer in all the vegetation zones, but the maximum of the individual numbers in forest-meadow zone and forest zone appeared in autumn. There were not only significant seasonal differences in density-group index in different vegetation zones (except in forest zone) but also differences in the composition and abundance of the dominant groups of soil animals in different seasons.