A microbicidal composition of 1,2-benzisothiazolin-3-one; and at least one of benzalkonium chloride, benzethonium chloride, benzyl alcohol, caprylyl glycol, chlorphenesin, diazolidinyl urea, ethylparaben, imidazolidinyl urea, methylparaben, phenoxyethanol, linoleamidopropyl PG-dimonium chloride phosphate, cocamidopropyl PG-dimonium chloride phosphate, propylparaben, cis-1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride, dehydroacetic acid or its salts, benzoic acid or its salts, and sodium hydroxymethylglycinate.