Four microbial communities capable of degrading acetochlor, designated A, D, E, and J, were obtained from acetochlor-contaminated soil and sludge. Acetochlor at an initial concentration of 55mg/L was completely degraded by the four mixed cultures after 4 days. At 80 mg/L acetochlor, more than 99% degradation was observed with D, 84% with A and E, and 88% with J after 9 days. There are primary eight strains of bacteria in community A, three in community D, E, and J, respectively. No single isolate was able to degrade acetochlor efficiently. The acetochlor biodegradation products were identified by gas chromatography-mass spectrometry. The probable degradative pathways of acetochlor involved dechlorination, hydroxylation, deethoxymethylation, cyclization, carboxylation, and decarboxylation. Propachlor, alachlor, and metolachlor, which are also the main components of the chloroacetanilide herbicide, could be degraded by the four mixed cultures to some degree. Given the high degradation rates observed here, the four mixed cultures obtained may be useful in the degradation processes of acetochlor.