Excessive use of thifensulfuron-methyl has raised concerns for environmental contamination and phytotoxicity to crops. Experiments were performed to isolate a microorganism that can degrade thifensulfuron-methyl and assess its effectiveness. A bacterial isolate, Ochrobactrum sp. ZWS16, capable of degrading thifensulfuron-methyl was studied. The half-life for thifensulfuron-methyl was less than 6 days in liquid medium after addition ZWS16 (5-400 mg thifensulfuron-methyl/l). Maximum biodegradation was 99.5 % for 50 mg thifensulfuron-methyl/l at 40 A degrees C over 10 days. Of the five metabolites from the degradation of thifensulfuron-methyl that were identified, methyl 3-(N-carbamoylsulfamoyl) thiophene-2-carboxylate and 3-[(formimidoylamino-hydroxy-methyl)-sulfamoyl)-thiophene-2-carboxylic acid are reported for the first time. The degradation pathways might proceed via cleavage of the sulfonylurea bridge, O-demethylation, de-esterification and cleavage of the triazine ring. The removal of thifensulfuron-methyl was 58 % after inoculation of strain ZWS16 into sterilized soil. Strain ZWS16 can also degrade nicosulfuron, tribenuron-methyl, pyrazosulfuron-ethyl, metsulfuron-methyl and triasulfuron. Addition of strain ZWS16 to both liquid medium and sterilized soil accelerated the degradation of thifensulfuron-methyl. Strain ZWS16 might therefore be useful in removing thifensulfuron-methyl contamination in water and soil.