An incubation study was conducted to investigate the effects of metsulfuron|methyl herbicide on the soil microbial biomass in loamy sand soil. The herbicide was applied to the soil at four concentrations: control, 0 01, 0 10, and 1.00 μg·g+{-1} soil. Determinations of microbial biomass|C and microbial biomass|N contents were carried out 1, 3, 5, 7, 10, 15, 25, and 45 days after herbicide application. In comparison to untreated soil, the microbial biomass|C and biomass|N decreased significantly in soils treated with herbicide at concentrations of 0.1 and 1 0 μg·g+{-1} soil within the first 7 days of incubation. The application of metsulfuron|methyl herbicide to the soil reduced the C-{mic}/C-{org} and N-{mic}/N-{total} percentages, which decreased with increasing application rate of metsulfuron|methyl herbicide. Compared to the untreated control, a marked increase in the microbial biomass C: N ratio was observed in the herbicide treated soil. This effect was transitory and was significant only at the higher rates of metsulfuron|methyl. An incubation study was investigating the effects of metsulfuron | methyl herbicide on the soil microbial biomass in loamy sand soil. The herbicide was applied to the soil at four concentrations: control, 0 01, 0 10, and 1.00 μg · g Determinations of microbial biomass | C and microbial biomass | N contents were carried out 1, 3, 5, 7, 10, 15, 25, and 45 days after herbicide application. In the untreated soil, the microbial biomass | C and biomass | N decreased significantly in soils treated with herbicide at concentrations of 0.1 and 1 0 μg · g + {- 1 } The application of metsulfuron | methyl herbicide to the soil reduced the C - {mic } / C - {org } and N - {mic } / N - {total } percentages, which decreased with increasing application rate of metsulfuron | methyl herbicide. Compared to the untreated control, a marked increase in the microbial biomass C : N ratio was observed in the herbicide t This effect was transitory and was significant only at the higher rates of metsulfuron | methyl.