A bacterial strain HZ-2 was newly isolated by enrichment culture from the activated sludge in a sewage treatment plant．Based on the morphology，the physiological and biochemical characteristics，and 16S rDNA sequence analysis，the strain HZ-2 was identified as Bacillus pumilus HZ-2．The strain HZ-2 could not only completely degrade mesotrione 200 mg/L in 5 d，under the conditions of 1% inoculum, 30 ℃, pH 7.0 and 180 r/min, but also could tolerate and efficiently degrade mesotrione of high concentrations up to 400 mg/L. All these results indicate the strain HZ-2 is deserved to be further developed as a candidate mesotrione-degrading microbe.