In this study, two different crystallographic phases of bismuth molybdate, α-Bi2Mo3O12and γ-Bi2MoO6were synthesized hydrothermally. A series of Bi2Mo3O12/Bi2MoO6heterostructures with different phase ratios were readily prepared by tuning the concentration of the molybdenum precursor while retaining the same bismuth precursor concentration. The Bi2Mo3O12/Bi2MoO6heterojunction was found to substantially enhance the photocatalytic water oxidation capability relative to neat Bi2Mo3O12and Bi2MoO6. The Bi2MoO6and Bi2Mo3O12were found to possess a complementary band alignment between which enabled the charge transfer process across the heterojunction interface. Ag and MnOxphotodeposition was conducted on the heterostructures to affirm the charge transfer direction between the two crystal phases. Under visible light irradiation, photogenerated holes transfer from the active Bi2MoO6phase to the inactive Bi2Mo3O12, suggesting efficient charge separation occurs between the two components, explaining the better photocatalytic performance.