In this study, KDL5 molecular distillation apparatus manufactured by the UIC Corporation was adopted to separate bio-oil, which came from a bench-scale fluidized-bed fast pyrolysis reactor at a feeding rate of 1 kg/h. A maximum distillate yield of 85% was obtained without obvious coking or polymerization during the molecular distillation process. The effect of distillation temperature on physical and chemical characterization of each bio-oil fraction was investigated. Statistical calculations showed that molecular distillation was successful in the separation of bio-oil. A separation factor was proposed to reflect the ability of isolating the chemicals contained in the bio-oil using molecular distillation. (C) 2009 Elsevier B.V. All rights reserved.