Abstract: Oriental Oak forest is widely distributed in 25˚—40˚N of China. Depending on the hydro-thermal condition of its area, this species grows well both in the Southern warm temperate zone and the northern Subtropical zone, in which the annual mean temperature is about 10˚—16℃ and rainfall reaches 500--1200mm.Oriental Oak is a heliophyllous tree. In Beijing, it mainly occurs at low hilly region with thin soil. Man’s activity are so frequent in the region that the physiognomy of natural Oriental Oak forest is uneven. The companion is Quercus dantata or Q. aliena. The shrub layer and herb layer are distinctive, the former being mainly composed of Vitex chinensis, Grewia biloba var. parviflora, Leptodermis oblonga, the latter being mainly composed of Clistogenes caepitosa, Carex nanella, Arundinella hirta, Themeda triandra var. japonica. In the planted Oriental Oak forest, the tree layer is of monospecies. The species and individual plants are less in number both in the shrub layer and herbaceous one.The biomass of a 26-aged planted Oriental Oak forest was determined at an altitude of 300m. of Xishan (Weat Mountain), in Beijing. The dry weight of each part of trees was obtained from ten sampling trees. Based on the power equation W=a(D2H)b, the data are as follows: trunk biomass 32.16 t/ha, branch biomass 9.85 t/ha, leaf biomass 1.68 t/ha, root biomass 9.95 t/ha. The biomass of shrubs and herbs obtained by harvest method are as follows: aboveground biomass of shrubs 1.33 t/ha, underground biomass of shrubs 2.3 t/ha; aboveground biomass of herbs 0.15 t/ha, underground biomass of herbs 0.8 t/ha. So the total aboveground biomass of the planted Oriental Oak forest is 45.17 t/ha, and the underground one is 13.05 t/ha, with the sum being 58.22 t/ha.