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Biodiversity patterns and their underlying mechanisms have long been focal topics of study for ecologists and biogeographers. However, compared with spatial variation in species richness (- and -diversity), -diversity, or the dissimilarity of species composition between two or more sites has until recently received limited attention. In this study, we explored the large-scale patterns of altitudinal turnover (-diversity) of plants in montane forests of China, based on systematic inventories of 1153 plots from 46 mountains distributed over 30 degrees of latitude (21.951.7 degrees N) and 4100 m of altitude (1604250 m). The -diversity of trees and shrubs declined significantly with increasing latitude. Along the altitudinal gradient, -diversity of both trees and shrubs showed non-significant trends in most mountains. Differences in climate explained 30.0% of the variation in tree -diversity (27.7, 36.5, and 26.2% for the Jaccard’s, j, Sorenson’s, s, and Simpson’s dissimilarity, sim, respectively), with mean annual temperature being most important, and 10.0% of that in shrub -diversity (10.0, 8.2, and 7.0% for j, s, and sim, respectively), with annual actual evapotranspiration and annual precipitation as the main predictors. However, climatic controls of -diversity varied dramatically in different biogeograpical regions. The -diversity of trees exhibited stronger, whereas that of shrubs showed weaker, climatic patterns in temperate and arid than subtropical regions. These results suggest that mechanisms causing patterns of -diversity may differ between latitudinal and altitudinal gradients, and among biogeographical regions; as a result, caution should be exercised in drawing close parallels between patterns and causes of -diversity along latitudinal and altitudinal gradients and among regions.