The present study investigated the seasonal changes in photosynthetic charateristics of co-occurring evergreen and deciduous broad-leaved trees in a montane evegreen broad-leaved forest in Yunnan Ailao Mountain and a montane decidous beech forest in Guangxi Mao′er Mountain in 2005, and tried to explore the effects of temperature climate differences between the two habiitas on species dominance. In summer, light-saturated photosynthetic rates per leaf area (Amax_a) exhibited no differences either between evegreen and deciodus species in each habitat or between the two habitats. However, as air temperature decreased, Amax_a of evegreen and deciodus species dropped in both habitats, resulting from partly stomatal closures and decreases of photosytem II activities. Stomatal closures could decrease water losses, but decidous spicies had higher degree of stomatal closures than evergreen species and were unavoidable to suffer heavier photoinhibition. Evergreen species could maintain green leaves by promoting photosynthetic water use efficiency through stomatal control and enhancing the ability of photosynthetic apparaturs via photosytem II adjustments. However, low tempertures in winter led to heavy malfunction of stomata and photosytem II and consequent low dominance of evergreen species in montane decidous beech forest in Mao′er Mountain. By contrast, relative warmness in winter helped evegreen species of montane evegreen broad-leaved forest in Ailao Mountain to acculmate more photosynthetic biomass and facilated them to dominate in the communities.