Condensed　and　low-defected　graphitic　carbon　nitride　(denoted　as　CNa)　was　synthesized　from　a　simple　one-step　thermal　polymerization　in　ammonia.　The　promotion　effect　in　the　structural　evolution　during　condensation　in　ammonia　and　catalytic　performance　for　H2　evolution　for　the　defected-C3N4　was　well　studied.　Comparing　to　pristine　g-C3N4　prepared　from　polymerization　in　nitrogen　(CNn),　the　as-prepared　sample　has　the　same　composition　and　graphitic　stacking　structure,　but　appears　well　dispersed　flake　morphology　with　larger　surface　area　and　more　mesoporous　texture.　Surprisingly,　this　sample　possessed　much　condensed　crystallinity　and　improved　in-plane　conjugated　network　with　decreased　sp2　N　defects　in　heptazine　heterocycle.　Consequently,　higher　rate　of　photocatalytic　H2　production　under　visible　light　irradiation,　about　6　times　of　CNn,　was　achieved,　owing　to　the　broader　distribution　of　active　sites　and　more　efficient　transport　and　separation　of　photogenerated　charge　carriers　in　the　improved　ordered　skeleton　microstructure.　©　2015　Elsevier　B.V.