A microbicidal composition containing: (a) 1,2-benzisothiazolin-3-one; and (b) at least one microbicide selected from among benzalkonium chloride, benzethonium chloride, benzyl alcohol, caprylyl glycol, chlorphenesin, 2,2'-dithiobis(N-methylbenzamide), diazolidinyl urea, ethylenediamine tetraacetic acid, 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, sodium hydroxymethylglycinate and zinc pyrithione.