Monolayer　HSr2Nb3O10　nanosheets　with　a　thickness　of　about　1.95　nm　were　synthesized　via　a　top-down　approach.　The　structure　and　morphology　were　well　characterized　by　XRD,　SEM　and　TEM　analyses.　The　sample　served　as　an　efficient　photocatalyst　for　hydrogen　evolution　with　the　in　situ　growth　of　highly　dispersed　Pt　clusters　(about　2　nm).　The　photocatalytic　hydrogen　evolution　rate　of　the　Pt/HSr2Nb3O10　nanosheets　was　530.2　μmol　gcatalyst-1　h-1　under　the　optimal　conditions　of　1　wt%　of　Pt　(PtCl4　as　the　precursor),　triethanolamine　(TEOA)　as　the　sacrificial　reagent　and　the　aqueous　solution　pH　=　10.7,　which　was　about　2.2　times　higher　than　that　of　the　layered　HSr2Nb3O10.　©　2019　The　Royal　Society　of　Chemistry.