To obtain the subject composition reduced and stabilized in skin irradiating property and improved in workability for injecting chemicals and storage stability by dissolving an isothiazolone compound and a specific compound into a solvent.

This antimicrobial composition is obtained by formulating (A) an isothiazolone-based compound of formula I or formula II [R is H, an alkyl or the like; X is condensed with Y to form a benzene ring; M is a cation of an alkali (earth)metal: Z is an anion forming a compound with M having solubility enough to form a complex compound; (a) is 1 or 2; (n) is an integer in which Z satisfies an atomic valence of M] (e.g. 5-chloro-2-methyl-4-isothiazolin-3-one) with (B) a compound capable of reducing skin-irritating property of the component A at (1:0.1) to 50 molar ratio of the component A to the component B and dissolving the mixture into (C) a solvent. A dicarboxylic acid, an aromatic carboxylic acid, a phenolic compound, an alcohol-based compound, an amide- based compound is preferable as the component B.