PROBLEM TO BE SOLVED: To obtain an antimicrobial agent composition high in safety and effects and wide in an antimicrobial spectrum, by including diiodomethyltolyl sulfone and dibromodicyanobutane. SOLUTION: This antimicrobial agent composition comprises diiodomethyl-p- tolyl sulfone and 1,2-dibromo-2,4-dicyanobutane in the weight ratio of 20:1 to 1:20, preferably 5:1 to 1:5, especially preferably 3:1 to 1:3. The total contents of these compounds is 0.1-95 wt.%, preferably 0.2-60 wt.% based on the whole composition. The antimicrobial agent composition preferably further contains a proper solvent (water, an alcohol, a ketone, an ether, an aliphatic or an aromatic hydrocarbon, a halogenated hydrocarbon, an acid amide, an ester, a nitrile, etc.), a dispersant such as a surfactant and a carrier (a clay, a talc, a silica, alumina, sulfur powder, active carbon, etc.).