[Objective] The aim of this study was to isolate anaerobic bacteria capable of degrading butachlor. [Methods] By enrichment and acclimation method using butachlor as carbon source for enrichment, we screened an anaerobic butachlor-degrading bacterium from paddy soil. The isolated strain was preliminarily identified based on morphological and biochemical characteristics as well as 16S rRNA phylogenetic analysis, and the metabolites of butachlor degradation were identified by liquid chromatography-time of flight mass spectrometry. [Results] An anaerobic bacterium designated as BAD-20 was screened and identified as Proteiniphilum. The optimum conditions for butachlor degradation by strain BAD-20 were 30-35 ℃, pH 7.5-8.0 and 0-0.5% NaCl. Under the optimal conditions, 90% butachlor was degraded within 10 days by Proteiniphilum sp. BAD-20. Under aerobic conditions, the stain lost the ability to degrade butachlor. Proteiniphilum sp. BAD-20 could also degrade alachlor, acetochlor and propionate with the degradation efficiency following the order: alachlor > acetochlor > propranolol > butachlor. The degradation kinetics to these chloroacetamide herbicides fit to a first-order kinetic equation. Two metabolites, N-(2,6-diethylphenyl)-N-(butoxymethyl)acetanilide and N-(2,6-diethylphenyl)acetamide, were identified, indicating that the initial two steps of butachlor degradation are dechlorination and dealkylation. [Conclusion] An anaerobic butachlor-degrading bacterium BAD-20 was enriched and isolated from paddy soil and identified as Proteiniphilum. This study provides a basis for further study on the anaerobic catabolism of butachlor and the development of anaerobic biological treatment technology for butachlor-containing wastewater.