Herein, we describe an uncommon example of a manganese-thiolate complex, which is capable of activating dioxygen and catalyzing its two-electron reduction to generate H2O2. The structurally characterized dimercapto-bridged Mn-II dimer [Mn-2(II)(LS)(LSH)]ClO4 ((Mn2SH)-S-II) is formed by reaction of the LS ligand (2,2'-(2,2'-bipyridine-6,6'-diyl)bis-(1,1-diphenylethanethiolate)) with Mn-II. The unusual presence of a pendant thiol group bound to one Mn-II ion in (Mn2SH)-S-II is evidenced both in the solid state and in solution. The (Mn2SH)-S-II complex reacts with dioxygen in CH3CN, leading to the formation of a rare mono-mu-hydroxo dinuclear Mn-III complex, [(Mn-2(III)(LS)(2)(OH)]ClO4 ((Mn2OH)-O-III), which has also been structurally characterized. When (Mn2SH)-S-II reacts with O-2 in the presence of a proton source, 2,6-lutidinium tetrafluoroborate (up to 50 equiv), the formation of a new Mn species is observed, assigned to a bis-mu-thiolato dinudear Mn-III complex with two terminal thiolate groups (Mn-2(III)), with the concomitant production of H2O2 up to similar to 40% vs (Mn2SH)-S-II. The addition of a catalytic amount of (Mn2SH)-S-II to an air-saturated solution of Me(n)Fc (n = 8 or 10) and 2,6-lutidinium tetrafluoroborate results in the quantitative and efficient oxidation of Me(n)Fc by O-2 to afford the respective ferrocenium derivatives (Me(n)Fc(+), with n = 8 or 10). Hydrogen peroxide is mainly produced during the catalytic reduction of dioxygen with 80-84% selectivity, making the (Mn2SH)-S-II complex a rare Mn-based active catalyst for two-electron O-2 reduction.