A　template-free　strategy　has　been　developed　for　the　controlled　synthesis　of　hierarchically　porous　gamma-Al2O3　with　three　dimensional　(3D)　＂cluster-like＂　architectures　assembled　from　2D　nanosheets　(similar　to　15　nm　thick).　This　unique　structure　endows　the　material　with　large　active　surface　area,　high　accessibility　and　ready　mass　transport　ability,　capable　of　promoting　the　catalytic　performance.　As　a　result,　the　designed　gamma-Al2O3　exhibits　high　activity　for　selective　oxidation　of　H2S　to　elemental　sulfur.　All　the　porous　gamma-Al2O3　samples　show　outstanding　sulfur　selectivity　(similar　to　100%)　below　200　degrees　C.　At　higher　temperatures,　the　H2S　conversion　increases　while　the　sulfur　selectivity　decreases.　The　maximum　sulfur　yield　(93%)　can　be　achieved　over　the　optimal　sample　at　240　degrees　C,　which　is　much　higher　than　those　of　commercial　alumina　and　most　of　the　reported　alumina-based　catalysts.　The　structure-activity　relationship　of　the　catalysts　has　been　systematically　studied.　It　is　demonstrated　that　the　surface　acidity　of　the　gamma-Al2O3　has　a　great　influence　on　catalytic　activity.　By　means　of　pyridine　and　H2S　in　situ　FTIR,　the　nature　of　the　active　sites　as　well　as　the　reaction　mechanism　of　H2S　selective　catalytic　oxidation　over　gamma-Al2O3　is　revealed,　providing　important　insights　into　the　design　of　alumina-based　materials　for　the　removal　of　sulfur-containing　compounds.