Bio®ltration is a cost effective air pollution control technology for volatile organic compounds. Bio®ltration of ethanol vapour from air stream was evaluated in this study. Experimental investigations were conducted on a laboratory scale bio®lter, containing mixture of compost and polystyrene inert particles as the ®lter materials. Mixed consortium of activated sludge was used as a inoculum. The continuous performance of bio®lter for ethanol removal was monitored for different concentrations and¯ow rates. The removal ef®ciencies decreased at higher concentrations and higher gas¯ow rates. A maximum elimination capacity of 195 g m A3 h A1 was achieved. The response of bio®lter to shut down and restart-up operation showed that the bio®lm has got a good stability.