Abstract: To investigate altitudinal changes of tree species biodiversity and community structures, we investigated 30 plots on the southeastern slope and 13 plots on the northwestern slope of Mt. Huanggang, Wuyi Mountains, Fujian Province. We recorded 151 tree species from 42 families and 73 genera on the southeastern slope, and 102 tree species from 32 families and 54 genera on the northwestern slope. There was no significant difference of tree species composition between these two slopes. The number of families, genera and species in the tree layer decreased as altitude increased. The richest families, genera and species were recorded at the altitudes between 800-1000 m a.s.l. on the southeastern slope, and between 1500-1600 m a.s.l. on the northwestern slope. The species diversity of tree layer on the northwestern slope was higher than that of the southeastern slope from 1200-1800m a.s.l.. ShannonWiener index (H′) correlated negatively with elevation on both slopes. Srenson index (IAc) varied in transitional zones between vegetation types, and was lowest at the ecotone between evergreen broadleaved forests and mixed coniferous and broadleaved forests. Considering community structures, larger maximum tree height (H_max) and maximum diameter of breast height (DBH_max) were recorded at middle elevations than at upper or lower elevations. Hmax and DBH_max were higher on the northwestern slope than on the southeastern slope at the same elevations. Total basal area (TBA) of evergreen broadleaved trees was greater than those of deciduous broadleaved trees and coniferous trees at low elevations. TBA of coniferous trees showed two peaks, corresponding to two different types of coniferous species while that of deciduous broadleaved species stayed stable along the altitudinal gradient. TBA of deciduous broadleaved trees was greater on the northwestern slope than on the southeastern slope. TBA patterns of these three life forms along the altitudinal gradient were similar on both slopes.