A simple method is developed to prepare cobalt phthalocyanine decorated BiVO4 composite photoanodes (CoPc(NH2)4/BiVO4). The photoelectrochemical (PEC) water oxidation activity of CoPc(NH2)4/BiVO4 composite catalysts is optimized by varying the loading content of CoPc(NH2)4. Under 1 sun illumination, the optimized 2CoPc(NH2)4/BiVO4 photoelectrode exhibits the largest photocurrent density of 3.02 mA/cm2 at 1.23 V vs. RHE in this study, which is 2.7, 1.6 and 1.4 times that of pure BiVO4, 1CoPc(NH2)4/BiVO4 and 3CoPc(NH2)4/BiVO4, respectively. The enhanced PEC water oxidation performance is ascribed to the synergistic effect between CoPc(NH2)4 and BiVO4 by improving reaction kinetics. The present study indicates that there is an optimum concentration of CoPc(NH2)4 in the composite catalysts to maximize the PEC water splitting performance, highlighting the influence of the loading content of CoPc(NH2)4 on the oxygen evolution reaction.