Identifying the active site of catalysts for the oxygen evolution reaction (OER) is critical for the design of electrode materials that will outperform the current, expensive state-of-the-art catalyst, RuO. Previous work shows that mixed Mn/Ru oxides show comparable performances in the OER, while reducing reliance on this expensive and scarce Pt-group metal. Herein, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy (XAS) are performed on mixed Mn/Ru oxide materials for the OER to understand structural and chemical changes at both metal sites during oxygen evolution. The results show that the Mn-content affects both the oxidation state and local coordination environment of Ru sites. Operando XAS experiments suggest that the presence of MnO might be essential to achieve high activity likely by facilitating changes in the O-coordination sphere of Ru centers.