Mixed Mn/Ru oxide thermally prepared electrodes using different compositions of Mn and Ru precursor salts have been fabricated on Ti supports via thermal decomposition at two annealing temperatures. Subsequently, the oxygen evolution reaction (OER) activities of these electrodes were determined. A majority of the mixed Mn/Ru catalysts are highly active for the OER, exhibiting lower overpotential values compared to those of the state-of-the-art RuO2 and IrO2 type materials, when measured at a current density of 10 mA cm–2. These Mn/Ru oxide materials are also cheaper to produce than the aforementioned platinum group materials, therefore rendering the Mn/Ru materials more practical and economical. The Mn/Ru catalysts are also evaluated with respect to their Tafel slopes and turnover frequency numbers. Interestingly, scanning electron microscopy reveals that the morphologies of the electrodes change to a mud-cracked morphology, similar to that of the RuO2, with minimal amounts of the Ru precursor salt added to the Mn salt. Fourier transform infrared spectroscopy and X-ray diffraction show that the Mn material fabricated in this study at the two annealing temperatures is largely Mn3O4, while the Ru material is predominately RuO2. X-ray photoelectron spectroscopy was also used to investigate the Mn and Ru composition ratios in each of the films.