Abstract: A microbiocidal composition comprising: a non-halogenated 2-alkyl-3-isothiazolone, and chlorphenesin and/or an alkane diol, wherein the alkyl group in the non-halogenated 2-alkyl-3-isothiazolone comprises 1 to 4 carbon atoms, the alkane diol comprises from 5 to 12 carbon atoms, and the hydroxyl groups of the alkane diol are vicinally substituted.