The　development　of　noble　metal　free　and　highly　active　cocatalysts　is　critically　important　and　also　challenging　for　the　practical　applications　of　photocatalytic　hydrogen　production.　Here,　ultrafine　MoO2　cocatalyst　nanoparticles　(≤10　nm)　were　in　situ　solvothermally　synthesized　on　carbon　nitride　nanosheets　(CNSs).　We　found　that　the　ultrafine　MoO2　nanoparticle　decorated　CNS　exhibits　higher　electrocatalytic　hydrogen　evolution　reaction　(HER)　performance　than　Pt-CNS.　Besides,　CNS　with　a　curly　thin　nanosheet　structure　has　an　increased　specific　surface　area　and　broadened　bandgap　after　the　solvothermal　process　compared　to　bulk　carbon　nitride　(CN).　Characterization　results　reveal　that　the　strong　interfacial　interaction　between　metallic　MoO2　and　CNS　greatly　promotes　the　photogenerated　electrons　extracted　from　CNS　to　MoO2,　resulting　in　efficient　electron　excitation　and　charge　transfer　in　the　composite.　Accordingly,　the　hydrogen　production　rate　of　1.0　wt%　MoO2/CNS　is　3.4　and　1.6　times　higher　than　that　of　the　same　mass　noble-metal　Pt　loaded　CN　and　CNS　under　visible　light　irradiation,　respectively.　This　work　may　provide　a　guide　for　constructing　non-noble　metal　cocatalyst　modified　materials　for　efficient　photocatalytic　hydrogen　production.　©　The　Royal　Society　of　Chemistry.