Rice husks are pyrolyzed in a fluidized bed reactor and the vaporized bio-oils are continuously graded into lighter and heavier bio-oils by in-line fractional distillation. The selection of the operating fluidization velocity is systematically discussed and the influences of the gas fluidization velocity on the physical and chemical properties of the graded oils are initially investigated. At the gas fluidization velocity of 0.46 m/s (1.3 U-mf) and pyrolysis temperature of 590 degrees C, aromatic compounds in the graded heavier oil, graded 20 degrees C trapped lighter oil and graded 0 degrees C trapped lighter oil are 68%, 38% and 15%, respectively. The best oil grading performance is obtained at 1.3 U-mf. The properties of the bio-chars are closely related to the gas fluidization velocity. Cleaner chars are obtained at 1.0 U-mf at the same pyrolysis temperature. The enhanced gas backmixing at higher gas fluidization velocity enhances secondary decomposition reactions. When the gas fluidization velocity increases from 1.0 Umf to 1.6 U-mf at the pyrolysis temperature of 490 degrees C, the water content and the heating value of the 20 degrees C trapped lighter bio-oils increases from 10% to 23% and decreases from 25.7 MJ/kg to 21.3 MJ//kg, respectively. (C) 2016 Elsevier Ltd. All rights reserved.