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Resource partitioning may allow species coexistence. Sand dunes in the typical steppe of Inner Mongolia, China, consist of desert, shrub and grass habitats, providing an appropriate system for studies of spatial niche partitioning among small mammals. We collected data to verify the niche separation hypothesis that coexisting small mammals would separate into spatial niches, and the productivity hypothesis that the highest species richness and overlap were to be expected in the most productive and diverse shrub habitat of the north-facing slopes, in contrast with the less productive grass and desert habitats of sand dunes. We trapped small mammals on 44 sand dunes in the summer of 1984 using snap traps. We captured 12 species of small mammals among three types of habitats. Cricetulus barabensis was a habitat generalist, present in all three types of habitats. Spermophilus dauricus was present only in the grass habitat, Allactaga sibirica and Dipus sagitta only in the desert habitat, and Apodemus peninsulae primarily in the shrub habitat. The shrub habitat hosted the largest number of small mammal species among the three types of habitats, supporting the productivity hypothesis. Habitat separation is an important mechanism for structuring small mammal communities in Inner Mongolia grasslands.