The field investigation data from 18 hilly areas in Hengduan Mountains of western Yunnan, China were accumulated and statistically analyzed in order to understand the basic distribution of the species richness and fauna pattern of fleas along altitudinal gradients, and ecological factors affecting their distribution. The altitude of areas investigated ranged from 1000 to 5000 m, and 142 species, 43 genera and 9 families of fleas were recorded. The analysis revealed that: (1) the genus richness, species richness, endemic species richness, ratios of endemic species and the species richness of different faunal realms gradually increased and then decreased with increase of elevation, such that a single-peak curve appears in vertical distribution. The peak appeared in the areas from 2500 m to 3800 m above sea level; (2) the vertical distribution pattern of Oriental fauna was quite different from that of Palaearctic fauna. The species components of Oriental fauna gradually decreased along the altitudinal gradient while those of Palaearctic fauna showed an increasing tendency, which reflected a pattern similar to that of the vertical distribution along the latitudinal gradient; (3)flea species in 9 vertical zones of Hengduan Mountains were classified into 6 ecological types by cluster analysis, which reflected the influence of some ecological factors (such as altitude, climate, and vegetation) on flea species distribution and community composition. It also demonstrated that flea distribution is in ac-cordance with the altitudinal gradient and environment. (4) A two-peak curve appeared in the vertical distri-bution of β diversity along an altitudinal gradient, which revealed a transitional fluctuation of flea species composition and distribution among the differential elevation, climate and vegetation zones. Both the bound-ary effect of transitional fauna or flora and the humidity may be the main reasons for the peak of species richness, genus richness and family richness in the middle elevation zones (2500-3800 m). We conclude that the pattern of flea distribution along an altitudinal gradient may be affected by a variety of factors, including altitude, the boundary effect of transitional fauna or flora, rainfall, climate, habitat, human ac-tivities, etc.