Abstract: This paper observed the tropical montane climate in Xishuangbanna of Southwest China,investigated the biomass of tropical montane rain forest in 5 plots (0.16～0.25 hm²) at the altitude of 1 100～1 820 m there,built the biomass regression equation and estimated the biomass of montane rain forest,and compared the results derived from the biomass regression equations of the tropical seasonal rain forest distributed at lower area and the montane rain forest.At the two altitudes of 1 105 and 1 610 m,the average annual temperature was 20.1 and 16.6 ℃,annual relative humidity was 81% and 84%,average annual rainfall was 1 659 and 2 011 mm,and the rainfall in dry season (from November to next April) was 295 and 283 mm,respectively.In the 5 plots,the biomass ranged from 256.4 to 368.6 t·hm^-2,with a mean of 312.6 t·hm^-2.The biomass of tree layer accounted for 97.1% of the total,and that of shrub,woody liana,and herb layers accounted for 1.3%,1.2% and 0.4%,respectively.Using the biomass regression equation of the tropical seasonal rain forest to estimate the biomass of montane rain forest would make the total biomass and the biomass of stem and root overestimated by 38.3%～61.5%,respectively,and make the branch biomass underestimated by 7.6%～30.8%.The results suggested that in the tropical montane rain forest in Xishuangbanna,the rainfall mostly occurred in rain season was increased with increasing altitude.The biomass of tropical montane rain forest was 32.6% lower than that of tropical seasonal rain forest,and the biomass regression equation derived from tropical seasonal rain forest was not suitable to the estimation of the biomass of tropica

Key words: Populus nigra, Volatiles, Steam distillation, GC-MS