The present study analyzed the photosynthesis-nitrogen relationship in evergreen and deciduous tree species at different altitudes on Mao'er Mountain, Guangxi, and explored whether photosynthetic nitrogen use efficiency (PNUE) was affected by leaf habit and altitude. Deciduous tree species had significanlty higher PNUE than evegreen tree species because of lower leaf mass per area (LMA) and higher photosynthetic rate per mass (A_mass), nitrogen content and stomatal conductance (g_s) in the former. Tree species at high altitude had significantly lower PNUE than those at middle and low altitudes due to higher LMA and lower A_mass and g_s in the former. Principal component analysis for PNUE and its related leaf traits suggested that the tree species distribution of evergreen-deciduous and low-middle-high altitude were in the process of natural transition. In addition, PNUE was not related to soil carbon: nitrogen ratio, but significantly positive related to mean annual temperature, suggesting that temperature climate was the main environmental factor that regulated the altitudianl changes in PNUE. Therefore, this differential PNUE that was affected by leaf habit and temperature climate was a mechanism for the bimodal distribution of evergreen tree species along the altitudes on Mao'er Montain.