High　thermal　stability　nanocrystalline　spherical　mesoporous　alumina　(NSMA)　and　ordered　mesoporous　alumina　(OMA)　were　synthesized　in　an　acetic　acid　assisted　sol-gel　system　by　adjusting　the　mole　ratio　of　n(acetic　acid)/n(Al)　and　synthesis　temperature　to　control　the　competition　between　the　colloidal　surface　free　energy　(F)　and　the　free　energy　of　mesostructure　self-assembly　(ΔG).　When　F　was　dominant,　with　the　mole　ratio　of　n(acetic　acid)/n(Al)　set　as　0.05-0.15　and　the　formation　and　aging　temperature　of　the　precursor　solution　set　at　30°C,　the　obtained　alumina　displayed　a　spherical　morphology,　and　the　nanocrystalline　spherical　mesoporous　alumina　dispersed　well　even　when　the　calcination　temperature　increased　up　to　1100°C;　however,　ordered　mesoporous　alumina　was　obtained　with　the　increasing　influence　of　ΔG　when　the　mole　ratio　of　n(acetic　acid)/n(Al)　was　set　as　0.10　and　the　lower　formation　and　aging　temperature　set　at　20°C,　and　it　retained　a　certain　ordered　structure　with　the　specific　surface　area　of　125　m2　g-1　even　when　the　calcination　temperature　increased　up　to　1000°C,　which　indicate　the　excellent　thermal　stability　of　its　pore　structure.　Taking　the　as-synthesized　aluminas　as　carriers,　Pd-supported　catalysts　were　obtained　and　their　catalytic　activity　for　CO　and　C3H6　oxidation　was　significantly　improved　compared　to　commercial　alumina.　©　The　Royal　Society　of　Chemistry.