PROBLEM TO BE SOLVED: To provide an antimicrobial agent capable of providing a fiber product preventing dirt of substrate or whitening generated during antimicrobial processing of a fiber product, and excellent in antibacterial property without generating dyeing specks, color omissions or dirt of can body of a dyeing tank even when antibacterial processing and dyeing are conducted in a same bath, and to provide an antimicrobial fiber product on which processing by the antibacterial agent for fiber is conducted.SOLUTION: An antibacterial agent for a fiber containing (A) pyrithione zinc, (B) polyoxyethylene arylphenyl ether sulfate ester, (C) polyethylene glycol fatty acid ester and/or (D) an aromatic sulfonic acid formaldehyde condensate, and (E) a thickener is used.
