Abstract: We analyzed changes in species diversity of plant communities on Mt. Mao'er using data from 16 plots, which were investigated along an altitudinal gradient at 100 m intervals. Each tree (DBH>3.3cm) was identified and recorded. Major results were summarized as follows: (1) A total of 184 tree species from 79 genera in 44 families, among which 121 were evergreen broadleaved, 61 were deciduous broadleaved and 2 were coniferous, were recorded. (2) Maximum height of tree layer and of different life forms decreased significantly with increasing altitude; however, maximum DBH, basal area and stem density were highest at midaltitudes. (3) Species richness did not change greatly below 1350 m but decreased sharply with an increasing altitude, with a peak at 1350 m. (4) Alpha diversity correlated with altitude in a similar but less significant fashion compared with species richness. Diversity (H′) correlated negatively with altitude, while evenness (E) did not change notably with altitude. (5) Similarity (C_J) between neighboring plots below 1350 m was larger than that above 1350 m, and the minimum similarity occurred in the transitional zone between different vegetation types. Species turnover (Cody index) paralleled patterns of community similarity (C_J). (6) In the study region, altitude seemed to be the primary determinant of community structure, species richness and alpha diversity, rather than slope and aspect. Spatial heterogeneity resulting from human disturbance and microlandform appeared to determine these characteristics at a local scale.