The imidazo[1,2-a]pyrimidines given by the following formula [I]: ##STR00001## [wherein R.sup.1 and R.sup.2 represent a C1 C6 alkyl group optionally substituted by one or more selected from the group consisting of C1 C4 alkoxy group, C2 C8 dialkylamino group, C1 C4 alkylthio group, C2 C5 alkoxycarbonyl group, cyano group and halogen atoms; or R.sup.1 and R.sup.2 represent a 3 8 membered heterocyclic group together with the nitrogen atom bonded with R.sup.1 and R.sup.2; R.sup.3 represents a halogen atom or C1 C4 alkyl group; and Ar represents a phenyl group optionally substituted by a halogen atom or atoms; and the like] have excellent activity for controlling plant diseases.