A laboratory incubation study was conducted to evaluate the effect of bensulfuron-methyl treatment on soil microbial biomass and N-mineralization of a loamy sand soil. The herbicide was applied at 0 (control), 0.01 (field rate), 0.1, and 1.0 microg g(-1), and soil microbial biomass carbon (C(mb)), soil microbial biomass nitrogen (N(mb)), and N-mineralization rate (k) were measured at different times after herbicide treatment. Compared to the untreated soil, C(mb) and N(mb) decreased significantly (p < or = 0.05) within the first 7 days after herbicide treatment at 0.1 and 1.0 microg g(-1), and the impact was greater for N(mb) than for C(mb). Nitrogen mineralization was significantly suppressed during the first 5 days of incubation when the soil was treated with bensulfuron-methyl at 0.1 and 1.0 microg g(-1). The overall impact of bensulfuron-methyl to the soil microbial communities was closely related to the application rate in the range of 0.01-1.0 microg g(-1). This effect, however, was found to be transitory, and significant impact occurred only at high application rates.