The hydroquinone peroxidase of a lignin decolorizing bacterium, Azotobacter beijerinckii HM121 degraded a water-insoluble synthetic polymer, polystyrene, in a two-phase system (dichloromethane-water), in which it was degraded in dichloromethane to small water-soluble molecules in a short time in the presence of hydrogen peroxide and tetramethylhydroquinone. Two grams per liter of polystyrene (M-r 935,000) in the dichloromethane phase was completely transferred to the water phase in 5 min by the enzymatic reaction. The degradation products in the water phase were initially detected at R-f 0.6 (M-r 1,000) in thin layer chromatography after reacting for 5 min, and then at R-f 0 (M-r 350) after reacting for 10 min. Another polystyrene (M-r 114,200) was degraded in a similar manner but low molecular weight polystyrene (M-r 760) was degraded and detected at R-f 0 without producing intermediate products at R-f 0.6 after 1-min reaction.