Fast pyrolysis is the most effective and commercially feasible technology for the production of bio-oil from biomass. Upgrading of lignin fraction bio-oil into liquid hydrocarbon is the main route for utilization of bio-oil. Increasing the amount of sugars in the aqueous fraction bio-oil will critically increase the importance of this fraction through conversion of sugars into more valuable liquid fuels and chemicals. In this study, a new application for membrane filtration technology to concentrate and separate sugars from aqueous fraction bio-oil was used. Green pinewood was pretreated with phosphoric acid under different acid concentrations and biomass/pretreating solution ratio to increase the yield of sugars in the bio-oil. The pretreated biomass was pyrolyzed in an auger reactor and the concentration of sugars in the bio-oil was determined by HPLC. The yield of sugars was increased from 15% to 25% at the optimum pretreatment condition. Lignin and aqueous fractions were fractionated from the bio-oil by adding an equivalent amount of water. Soluble phenolic compounds were removed from the aqueous fraction through solvent-solvent separation step using n-butanol or ethyl acetate. The produced sugar rich aqueous fraction was concentrated with Alfa Laval M20 membrane filtration system using Reverse Osmosis (RO) membranes. The concentrated sugar solution was dried by freeze dryer and the remaining sugars were isolated. (C) 2012 Elsevier B.V. All rights reserved.