The study was carried out at Agroforestry Research Centre, G.B. Pant University of Agriculture and Technology, Pantnagar, during 2010-11 to study the effect of tree densities on soil physico-bio-chemical properties under eight year old poplar based agrisilvicultural system. Treatment consisted of four tree densities as main plot and four soil depths as sub-plot were studied in split plot design with three replications.Poplar tree density showed significant effect on soil physico- chemical and biological properties of soil profile. The soil bulk density was significantly lower under trees compared to sole crop.The soil chemical properties viz., carbon, organic carbon, available nitrogen, available phosphorus, exchangeable calcium, DTPA extractable zinc, copper and manganese were significantly higher under trees than sole crop. The improvement in the soil physico- chemical and biological properties under the trees can be attributed to higher amount of biomass addition through litter fall and fine root recycling under trees compared to sole crop. Thus it can be concluded that soil properties were significantly improved under poplar based agroforestry system than sole crop.