Catalyst HZSM-5 was used in bio-oil catalytic cracking upgrading. The precursor of coke on the catalyst was analyzed by means of TGA, FTIR and C13 NMR. Precursors of coke deposited in the pore of the molecular sieve were mainly aromatic hydrocarbon with the boiling point range from 350 degrees C to 650 degrees C. Those on the outer surface of the pellet precursor were identified as saturated aliphatic hydrocarbons with the boiling point below 200 degrees C. The activity of HZSM-5 was studied after regeneration. In terms of yield of organic distillate and formation rate of coke, results showed that catalytic activity change moderately during the first three times of regeneration. (C) 2009 Published by Elsevier Ltd.