Reduced　graphene　oxide　(RGO)/ZnIn2S4　nanocomposites　with　RGO　in　different　reduction　degrees　have　been　prepared　and　their　photocatalytic　performance　for　H-2　evolution　under　visible　light　irradiation　has　been　evaluated.　The　reduction　degree　of　RGO　in　the　RGO/ZnIn2S4　nanocomposite　synthesized　via　a　direct　hydrothermal　process　was　low　and　the　resultant　RGO/ZnIn2S4-hydrothermal　exhibited　lower　photocatalytic　performance　for　H-2　evolution　even　when　compared　to　pure　ZnIn2S4.　The　reduction　degree　of　RGO　in　the　RGO/ZnIn2S4　nanocomposite　can　be　increased　by　a　further　photoreduction　or　hydrazine　reduction.　These　highly　reductive　RGO/ZnIn2S4　nanocomposites　showed　significantly　enhanced　photocatalytic　activity　for　H-2　production　under　visible　light　irradiation.　Highly　reduced　RGO　in　the　RGO/ZnIn2S4　nanocomposites　serves　as　a　good　electron　acceptor/mediator　as　well　as　the　H-2　evolution　site　to　promote　the　photocatalytic　water　splitting　over　ZnIn2S4.　A　correlation　between　the　photocatalytic　performance　for　H-2　evolution　and　the　RGO　reduction　degree　over　RGO/ZnIn2S4　nanocomposites　was　shown　for　the　first　time.　This　study　provides　new　insights　in　the　developments　of　RGO-based　nanocomposite　materials　for　photocatalytic　applications.