Atomically　precise　metal　nanoclusters　(NCs)-based　photocatalytic　systems　have　garnered　enormous　attention　owing　to　the　fascinating　merits　including　unique　physicochemical　properties,　quantum　confinement　effect,　and　photosensitization　effect,　which　are　distinct　from　conventional　metal　nanocrystals　(NYs).　Nevertheless,　a　systematic　comparison　between　electrons　photoexcited　from　metal　NCs　and　hot　electrons　from　surface　plasmonic　resonance　(SPR)　effect　of　metal　NYs　in　boosting　photoelectrochemical　water　splitting　reaction　remains　blank.　Here,　we　report　the　strict　and　comprehensive　comparison　on　the　capability　of　electrons　photoexcited　from　glutathione-capped　gold　nanoclusters　(Aux@GSH)　and　hot　electrons　from　plasmonic　excitation　of　gold　nanoparticles　(Au　NYs)　self-transformed　from　Aux@GSH　to　trigger　the　photoelectrochemical　(PEC)　water　splitting　reaction　under　visible　light　irradiation.　The　results　indicate　that　photoelectrons　of　Aux　NCs　trigger　a　more　efficient　charge　transport　rate　than　hot　electrons　of　plasmonic　Au　NYs　in　terms　of　light-harvesting　and　conversion　efficiency　under　identical　conditions.　Moreover,　charge　transfer　characteristics　in　Aux　NC-　A　nd　Au　NY-based　PEC　systems　were　established.　This　work　would　reinforce　our　deep　understanding　of　these　two　pivotal　sectors　of　metal　nanomaterials　for　solar　energy　conversion.　Copyright　©　2020　American　Chemical　Society.