N-acylimidazole represented by the formula: ##STR1## wherein R is a lower alkyl group, and X, Y and Z are, the same or different, each a hydrogen atom, a halogen atom, a lower alkyl group, a halogenated lower alkyl group, a lower alkoxy group, a lower alkylthio group, a cyano group or a nitro group, or two of X, Y and Z, taken together, may form a methylenedioxy group, which is useful for controlling plant diseases.