Adsorption of a dinuclear μ-oxo bridged Mn complex onto mesoporous silica was observed when SBA15 was treated with an acetonitrile solution of [Mn₂(μ-O)₂Cl(μ-O₂CCH₃)(H₂O)(bpy)₂](NO₃)₂ (1). This complex was immobilized via the displacement of NO₃⁻ into solution, and characterization by spectroscopic (DRIFTS and DRUV-vis) and magnetic data indicates that the intact dication is electrostatically bound to the silica surface. Loadings of up to 4.1% by weight of [Mn₂(μ-O)₂Cl(μ-O₂CCH₃)(H₂O)(bpy)₂]²⁺ were achieved. TEM images of the grafted material revealed retention of the mesoporous structure of SBA15, and no clusters of manganese greater than ca. 10 nm were observed. The SBA15-supported dimanganese complex functions as a catalyst for the oxidation of H₂O with (NH₄)₂Ce(NO₃)₆ as stoichiometric oxidant. In contrast, homogenous aqueous solutions of 1 do not evolve oxygen upon treatment with (NH₄)₂Ce(NO₃)₆. Labeling studies with H₂¹⁸O confirm that the oxygen formed in this catalysis is derived from water. Monitoring the O₂ evolution allowed determination of an initial rate for the catalysis (TOF_i = 1.1 × 10⁻³ s⁻¹). These studies also reveal a first order dependence on manganese surface concentration, and a zero order rate dependence for (NH₄)Ce(NO₃)₆. Spectroscopic investigations were employed to investigate the difference in activities between dissolved and supported dimanganese complexes.