This paper presents the use of Ca2Mn2O5 as an oxygen-deficient perovskite electrocatalyst for oxygen evolution reaction (OER) in alkaline media. Phase-pure Ca2Mn2O5 was made under mild reaction temperatures through a reductive annealing method. This oxygen deficient perovskite can catalyze the generation of oxygen at ~1.50 V versus (vs) reversible hydrogen electrode (RHE) electrochemically, and reach an OER mass activity of 30.1 A/g at 1.70 V (vs RHE). In comparison to the perovskite CaMnO3, Ca2Mn2O5 shows higher OER activities. The molecular level oxygen vacancies and high spin electron configuration on manganese in the crystal structures are likely the contributing factors for the enhanced performance. This work demonstrates that oxygen-deficient perovskite, A2B2O5, is a new class of high performance electrocatalyst for those reactions that involve active oxygen intermediates, such as reduction of oxygen and OER in water splitting.