Thermal and oxidative cracking of volatiles from the rapid pyrolysis of sawdust were studied at 700 and 800 °C using a novel two-stage reactor that enabled to observe vapor-phase secondary reactions of nascent volatiles separately from the primary pyrolysis. A particular focus was made on combined effects of temperature and air ratio on the yield, composition and then condensability at 350–500°C of residual tar. The condensability was evaluated by the amount of tar deposits over a type of ceramic fiber filter at reactor downstream per that of the residual tar. Experimental results showed clear differences in the behaviors of O₂ and the tar between 700 and 800 °C. The thermal cracking at 700°C allowed heavy tar (molecular mass; > 500) to escape from the reactor, and the partial oxidation was therefore indispensable for decomposing it. A substantial portion of O₂ reacted with the tar of that yield decreased with increasing air ratio. The condensability, however, changed little in a range of air ratio up to 0.2, and a ratio as high as 0.4 was required to reduce the condensability to 1/5 of the tar without oxidation. The thermal cracking took place very rapidly at 800°C producing light gases and refractory aromatics with molecular mass < 500. As a result, O₂ was consumed by oxidation of light gases exclusively, and then the tar yield was nearly independent of the air ratio. The thermal cracking at 800°C thus decreased the condensability of the tar to a negligible level without oxidation.