MoS2/ZnIn2S4　nanocomposite　was　prepared　via　photoreduction　of　(NH4)(2)MoS4　in　the　presence　of　hexagonal　ZnIn2S4.　The　as-obtained　MoS2/ZnIn2S4　nanocomposite　showed　superior　activity　for　acceptorless　photocatalytic　semi-dehydrogenation　of　1,2,3,4-tetrahydroisoquinoline　to　produce　3,4-dihydroisoquinoline,　with　quantitative　hydrogen　evolved.　In　addition　to　MoS2/ZnIn2S4,　a　series　of　MS/ZnIn2S4　nanocomposites　(MS　=　PtS　and　NiS)　were　also　found　to　be　active　for　this　reaction,　indicating　that　ZnIn2S4-based　nanocomposites　are　effective　photocatalysts　for　acceptorless　semi-dehydrogenation　of　1,2,3,4-tetrahydroisoquinoline　to　produce　3,4-dihydroisoquinoline.　This　study　not　only　provides　an　efficient,　green　and　cost　effective　strategy　to　produce　3,4-dihydroisoquinoline,　but　also　highlights　the　great　potential　of　semiconductor-based　photocatalysis　for　light-driven　organic　syntheses.