PURPOSE: To provide an industrial microbicidal composition having excellent preparation stability and capable of suppressing the crystallization of diols, the lowering of the microbicidal action with lapse of time and the formation of slime by mixing a microbicide for preventing slime trouble with a specific hydrocarbon solvent and a hydrophilic solvent.

CONSTITUTION: This liquid industrial microbicidal composition is produced by adding 4,5-dichloro-1,2-dithiol-3-one of formula III as an active microbicidal component for preventing slime trouble to a mixed solvent composed of a hydrophilic organic solvent and one or more kinds of aromatic hydrocarbons selected from the compounds of formula I and formula II (R1 is H or methyl; R2 to R6 are each a 1-4C alkyl). The compound of formula I is preferably 1- phenyl-1-(2,3-dimethylphenyl)ethane, etc., and the compound of formula II is preferably 1,7-dimethyl-3-propylnaphthalene, etc. The hydrophilic organic solvent is preferably dimethylformamide, ethylene glycol, etc. The composition can be dispersed in the form of small oil droplets by adding to water and the diol is slowly dissolved from the droplets to sterilize the system.