A simultaneous analytical method based on LC-MS/MS was developed for the determination of flufenacet and its metabolites, [(4-fluorophenyl)(1-methylethyl) amino]oxo-acetic acid and [N-(4-fluorophenyl)-N-(1-methylethyl) acetamide]-2-sulfinylacetic acid, in agricultural products. The compounds were extracted from samples with methanol. The crude extracts were purified using Bond Elut C18 and InertSep GC/PSA, then determined by LC-MS/MS. The average recoveries (n=5) from 4 kinds of agricultural products (wheat, soybean, potato and tomato) spiked at the level of the MRLs or the uniform limits (0.01 μg/g) were 70.6–97.0%, and the relative standard deviations were less than 5%. The lower limits of quantitation of flufenacet and its metabolites were 0.01 μg/g.