Abstract: Objective To investigate the distribution pattern，species diversity and community structure of fleas on small mammals in the surrounding area of Erhai Lake, and the relationship between fleas and their hosts. Methods Different geographical areas surrounding the Erhai Lake in Yunnan were selected as investigated spots. Small mammals were captured with baited cages. The cage-traps were examined and re-baited each morning. All fleas on the hosts were collected and identified. The richness （S）, evenness （J′）, diversity index （H′）, dominance index （C′）, total ectoparasite infestation rate （Rpt）, total ectoparasite infestation index （Ipt）, and constituent ratio （Cr） were used to measure the community structure. Results Althgether, 3 303 small mammals and 3 243 fleas were collected. From the 21 species of small mammal hosts, 13 species of fleas were identified. In southern area of the Lake, the species richness （21 species of small mammals & 12 species of fleas） was highest among the three selected areas. Seventeen species of small mammals and 8 species of fleas were found in eastern area, and only 13 species of small mammals and 7 species of fleas found in the west. This implied the probable influences of ecological environments on the fleas and their corresponding hosts. The community structure of fleas on small mammals was complex. The species diversity, species composition, community structure and distribution pattern of fleas were simultaneously influenced by the hosts' body surface microenvironment and the macroenvironment （habitat）. Conclusion The fleas are commonly distributed in small mammals in the areas and their communities are related to host species and the habitats.

Key words: Siphonaptera, Flea, Community ecology, Co-evolution, Small mammal, Erhai Lake