Abstract:The seedlings of 4 dominant tree species of tropical seasonal rain forest, such as Pometia tomentosa, Barringtonia macrostachya, Myristica yunnanensis and Knema globularia, were transplanted at three altitudinal sites (low 600 m in Menglun; middle 1 100 m in Caiyanghe; high 1 600 m in Mengsong) in Xishuangbanna. The parameters of photosynthesis and biomass of these seedlings were measured. The results showed that the low temperature at high altitude caused dormancy or photosynthetic system destroy. The maximum photosynthesis rate (Pmax) and dry biomass of four seedlings declined significantly along the increment of elevation. The diurnal change pattern of photosynthetic rate of four seedlings at low and middle altitude both showed double-peak type, which the first peak appeared at 11: 00~12: 00 am and the next peak at 4: 00~5: 00 pm, and the first peak was higher significantly at low altitude than that at middle altitude. Except for K. globularia, the root biomass fraction (RMF) of seedlings of the others increased with the increment of altitude. It is concluded that the biomass and photosynthetic rate of these seedlings are mainly limited by temperature, which is the potential reason that these species disappeared in rain forest community at high altitude. Furthermore, It is an important characteristic adapted to limited environmental temperature that RMF of four seedlings increased with the increment of altitude.