Nitric　oxide　(NO)　emitted　from　the　combustion　of　fossil　fuels　has　drawn　global　concern,　and　the　oxidation　of　NO　contributes　greatly　to　the　DeNO(x)process.　Herein,　single-crystal　gamma-MnO(2)catalysts　with　well-defined　hollow-sphere-,　sea-urchin-,　and　flower-like　morphologies　(gamma-MnO2-HS,　gamma-MnO2-SU,　and　gamma-MnO2-F)　were　rationally　designed　and　synthesizedviaan　environmental-friendly　template-free　hydrothermal　strategy.　The　physicochemical　properties　of　the　prepared　materials　were　characterized　by　XRD,　FE-SEM,　TEM,　BET,　XPS,　H-2-TPR,　O-2/NO-TPD　andin　situDRIFTS,　and　their　catalytic　activities　in　NO　oxidation　were　evaluated.　The　results　showed　the　gamma-MnO2-HS　sample　possessed　the　highest　activity　and　could　oxidize　91.1%　of　NO　at　275　degrees　C,　which　was　obviously　higher　than　those　of　the　gamma-MnO2-SU　and　gamma-MnO2-F　catalysts.　It　was　found　that　the　presence　of　abundant　surface-adsorbed　oxygen　and　the　largest　quantity　of　Mn(3+)over　the　gamma-MnO2-HS　material　respectively　accelerated　the　processes　of　NO　adsorption　and　O(2)activation,　which　greatly　promoted　the　NO　oxidation　process.　This　work　provides　significant　insights　into　NO　oxidation　over　gamma-MnO(2)catalysts.