The experiments on the rice husk pyrolysis were performed in a fixed-bed reactor to produce bio-oil. The effects of the different operation factors such as pyrolysis temperature sweeping gas (N-2) flow rates and ZnO catalyst on the yields of three products and the characteristics of bio-oil were investigated. The maximum bio-oil yield of 49.91% was obtained at 550 degrees C pyrolysis temperature with a heating rate of 25 degrees C/min and nitrogen flow rate of 150 mL/min. The bio-oils yielded with and without a catalyst were characterized by FT-IR and GC/MS. The results showed that the main identified compounds of bio-oils were phenols, phenol derivatives and long-chain aliphatic compounds. It was observed that the use of catalyst decreased the bio-oil yields, but enhanced the small molecular compound yields and decreased the amount of oxygenated groups in bio-oils. A series of rheological tests were performed for the two kinds of bio-oil with cone and plate rheometer. The results indicated that both types of bio-oil were typical non-Newtonian and strongly shear thinning liquids in the flow behavior. The viscosity of the ZnO-treated bio-oil was significantly lower than that of the bio-oil without any catalyst. (c) 2012 Elsevier B.V. All rights reserved.