A biocidal composition containing, as active ingredients, at least one imidazole compound represented by formula (I): ##STR1## wherein R.sup.1 represents a phenyl group, a halogen-substituted phenyl group, an alkyl group, or a halogen-substituted alkyl group; and R.sup.2 represents a halogen atom, and at least one other specific compound. The combination of the compound represented by formula (I) and other specific compound can produce an unexpected effect in amount required and biocidal spectrum.