The organosulfur compounds allicin, methionine and methylcysteine protect against metal-mediated oxidative DNA damage, but few studies have determined the antioxidant behaviour of the oxo-sulfur derivatives of these compounds. Gel electrophoresis experiments were performed to determine the ability of MetSO, MeCysSO, MMTS, MePhSO and Me2SO2 to inhibit copper- and iron-mediated DNA damage. Under these conditions, MetSO and MeCysSO significantly inhibit DNA damage, MePhSO and Me2SO2 have no effect and MMTS promotes DNA damage. For iron-mediated DNA damage, significantly less antioxidant or pro-oxidant behaviour is observed for these compounds. To determine whether metal coordination is a mechanism for the antioxidant activity of these oxo-sulfur compounds, UV–vis spectroscopy and gel electrophoresis experiments using [Cu(bipy)2]+ or [Fe(EDTA)]2− as the metal source were also performed. Results of these experiments indicate that metal coordination is a significant factor for their antioxidant activity, but another mechanism also contributes to their antioxidant behaviour.