The stability of porous coordination polymers during an electrochemical reaction could be improved by introducing supporter materials. An I3O0-type inorganic hybrid electrocatalyst, cobalt cinnamate, supported on reduced graphene oxide (rGO) was successfully prepared for an oxygen evolution reaction. The electrocatalytic activity and stability of cobalt cinnamate(catalyst)/rGO composite were significantly improved due to the strong interaction between catalyst and supporter, which led to enhanced anchoring stability and electrical conductivity. The catalyst/rGO composite shows ~30 mV reduction in overpotential and improvement in durability from ≥35% to ≥70% after a reaction time of 12 h, compared to the catalyst alone.