The anaerobic degradation of 2-propanol in anoxic paddy soil was studied with soil cultures and a 2-propanol-utilizing methanogen. Acetone was the first and the major intermediate involved in the methanogenic degradation of 2-propanol. Analyses with a methanogenesis inhibitor, bacteria antibiotics, and the addition of H-2 to the gas phase revealed that 2-propanol oxidation to acetone directly occurred using 2-propanol-utilizing methanogens, but not with H-2-producing syntrophic bacteria, for which the removal of acetone is required for complete 2-propanol oxidation. The 2-propanol-utilizing strain IIE1, which is phylogenetically closely related to Methanoculleus palmolei, was isolated from paddy soil, and the potential role of the strain in 2-propanol degradation was investigated. 2-Propanol is one of the representative fermentation intermediates in anaerobic environments. This is the first report on the anaerobic 2-propanol degradation process.