PROBLEM TO BE SOLVED: To provide an effective antiseptic mildew-proofing agent that can be jointly used with an isothiazoline compound. SOLUTION: The antiseptic mildew-proofing agent composition for water-based industrial products comprises 2-chloroacetamide and at least one selected from the group consisting of 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, and salts thereof. The composition exhibits excellent antiseptic mildew-proofing properties against microorganism and can stably preserve water-based industrial products such as paints, adhesives, pressure-sensitive adhesives, silicone emulsions, industrial detergents, textile oily agents or metal-working oils. Moreover, the composition generates no formaldehyde. COPYRIGHT: (C)2007,JPO&INPIT