Air-lift biofilm reactor should be an admirable process substituting conventional activated sludge process, because of its small area requirement as well as high volumetric loading capacity and stability against loading and chemical shocks. However most of the past research on the performance of ABR was focused on the sewage treatment. This research studied the applicability of ABR to treat high strength wastewater. A bench-scale ABR was operated to treat high strength synthetic wastewater, tannery wastewater and petrochemical wastewater, and its applicability was conclusive. In case of synthetic wastewater, ABR showed good performance in which the substrate removal efficiency was higher than 80 % even under short HRT(1.4 hr) and high volumetric loading rate(9.3 ㎏CODcr/㎥ day). When ABR was applied to treat tannery wastewater, it was suggested that the maximum volumetric loading rate and F/M ratio should be 7.7 ㎏CODcr/㎥ day, 0.76 day-1, respectively. And high substrate removal efficiency over than 90 % was observed with 4,000 ㎎CODcr/L of petrochemical wastewater. Even though effluent concentration was quite high, ABR should be applicable to treat the high strength wastewater, because of its high loading capacity.