In this study, pyrolysis process of wood bio-oil was studied. The effects of temperature in the range 550- 1000 _C, heating rate in the range 2-2000 _C s_1 and ash content of the bio-oil on char, tar and gas yields were investigated. The main gas species generated are quantified by Micro-GC: H2, CO, CO2, CH4 and trace amounts of C2H4 and C2H6. A temperature increase from 550 to 1000 _C enhanced greatly the gas yield, whilst solid and liquid yields decreased significantly. The heating rate was varied in a range covering rapid pyrolysis using the Horizontal Tubular Reactor (HTR) to flash pyrolysis using an Entrained Flow Reactor (EFR). A decrease of char yield from 11 wt.% down to 4 wt.% was observed when heating rate is changed from 2 to 100 _C s_1. In EFR a flash heating rate of 2000 _C s_1 led to a char yield as low as 1 wt.%. Bio-oil with a natural ash contents of 0.05 wt.% and bio-oil added with 3 wt.% of ash were finally pyrolyzed. Ash seems to favor re-polymerization reactions that lead to an increase in char yield. A decrease in the amount of gas is observed when ash is added while an increase was a priori expected.