The transformation of prosulfuron [1-(4-methoxy-6-methyltriazine-2-yl)-3-[2-(3,3,3-trifluropropyl)phenylsulfonyl]urea] in three soils at different pH values (sterilized and unsterilized) was studied, and it was shown that the rate of transformation was high in acidic soil. From the results obtained in sterile soils, it is shown that the mechanism of dissipation was mainly chemical in acidic soils. A new metabolite, 2-(3,3,3-trifluoropropyl)phenylsulfonic acid, was identified.