A bacterial strain S9-1 capable of degrading sulfonylurea herbicide pyrazosulfuron-ethyl (PSE) was isolated from contaminated soil through the enrichment incubation method. Based on morphology, colony and cultural properties, physiological and biochemical characteristics, living-cell absorption spectra, internal photosynthetic membrane, and phylogenetics of its 16S rRNA gene sequence, S9-1 was preliminarily identified as belonging to the genus Rhodopseudomonas, a group of photosynthetic bacteria (PSB). The effects of PSE concentration, pH, and temperature on biodegradation were examined. The degradation rate was found to decrease with increasing PSE concentration. Optimal growth pH and temperature were found to be 7.0 and 30°C, respectively. The strain was able to degrade 47.51% of PSE at a concentration of 100 mg ml-1 after 7 days of incubation at 30°C and could tolerate 800 mg ml-1 PSE. S9-1 was also able to completely co-metabolically transform 100 mg ml-1 PSE at 30°C, pH 7.0, and 7500 lux in 15 days. As the concentration of PSE increased, the degradation process took longer to complete. The fragment encoding acetolactate synthase (ALS) gene from S9-1 was cloned and sequenced. Comparison of deduced amino acid sequences was implemented, and the conserved sites were analyzed. To our knowledge, this is the first report of PSB in PSE biodegradation. These results highlight the potential of this bacterium as a detoxifying agent for use with PSE-contaminated soil and wastewater.