A series of 1-acyl-3-isopropenylbenzimidazolone derivatives were synthesized, and their structures were characterized by (1)H and (13)C NMR and elemental analysis. Their fungicidal activities against Botrytis cinerea were also evaluated by spore germination assay. The acrylic acid, methacrylic acid, 4-chlorophenyl acetic acid, and 2-chlorobenzoic acid derivatives exhibited strong fungicidal activity. This implied that benzimidazolones might be potential fungicide leading compounds.