One strain of bacterium IM-4, capable of degrading imazethapyr (IMZT), was isolated from the IMZT-contaminated soil. The isolate was identified as Pseudomonas sp. according to its physiological characteristics, biochemical tests, and 16S rRNA gene phylogenetic analysis. This strain could utilize IMZT as the sole carbon and energy source. About 73.4% of the 50 mg l(-1) initially added IMZT was degraded after 7 days of inoculation with strain IM-4. This strain also showed the capability to degrade other imidazolinone herbicides such as imazapyr, imazapic, and imazamox. The inoculation strain IM-4 to soil treated with IMZT resulted in a higher degradation rate than in noninoculated soil regardless if the soil was sterilized or nonsterilized. Inoculation of strain IM-4 could also mitigate the phytotoxic effects of IMZT on the growth of maize.