The structure-activity relationship in the electrochemical OER has been studied widely, but aspects of the photoelectrochemical (PEC) O2 evolution activity with different manganese oxides are not fully explored. In the present study different manganese oxides (MnO2, MnOx (a mixture of Mn3+ and Mn4+ ions), Mn2O3, and Mn3O4) have been electrodeposited onto the BiVO4 photoanode as co-catalysts for PEC water splitting. We find that BiVO4-MnOx shows the lowest onset potential of 0.33 V vs. RHE and the highest activity among the manganese oxides. Annealing at different temperatures results in the improvement of the OER kinetics at the interface with some detrimental effect on the activity of BiVO4. Such a study may lead to useful changes in the fabrication of semiconductor thin film photoelectrodes useful for PEC water splitting.