A synergistic antimicrobial composition. The composition contains at least two components. The first component is ortho-phenylphenol or its alkali metal or ammonium salts. The second component is: 4, 4 - dimethyloxazolidine (DMOZ), tris (hydroxymethy) nitromethane or hexahydro- 1,3,5-tris (2 -hydroxyethyl) - s - triazine.