Oxygen evolution reaction (OER) electrocatalysts suitable to work in acid are typically restricted to platinum group noble metal oxides because of their high activity and, especially, stability. Co3O4 is currently explored as an alternative OER catalyst. Herein we prepared Co3O4 films on fluorine‐doped Sn oxide (FTO) glass and Ti foil via thermal decomposition of nitrate salts and evaluated their activity and stability in 0.05 M H2SO4. Crystalline Co3O4 films deposited on FTO were stable during chronopotentiometry at 10 mA cm−2 for over 16 hours. The dissolution rate was 61 ngCo cm−2 min−1. The choice of a stable support such as FTO is essential to ensure the stability of the catalyst‐substrate interface and to prevent substrate passivation under OER conditions. Doping Co3O4 with Li resulted in a higher OER activity under acidic conditions to be attributed to the larger electrochemical surface area, although the stability was impeded compared to undoped Co3O4.