This talk will discuss the multiple roles of gold nanoparticles in photocatalysts. First, the gold nanoparticle can serves as the plasmonic photosensitizers for enhancing the solar energy conversion. Second, the gold nanoparticles can act as the electron relays for facilitating the electron transfer between the quantum dots and semiconductors. Third, the gold nanoparticle can work as the electron sinks due to the Fermi equilibration effect. In addition, this presentation will discuss how to distinguish all the effects of gold nanoparticles in photocatalysis.