Abstract Boehmite was calcined with and without steam at temperatures in the range 550°-100°. Hydrothermal treatments yielded structures with more well-developed crystallinity and pore sizes distributed around larger average pore sizes than did thermal treatments. Pt and Pt+ Rh were deposited on hydrothermally and thermally treated alumina by direct impregnation and ion exchange. The chemisorption of hydrogen on these metals was about 50% lower on hydrothermally treated than on thermally treated supports. Platinum applied by direct impregnation on hydrothermally treated alumina had lower light-off temperatures and were more efficient catalysts for oxidation of carbon monoxide, propene, xylene and propane than on thermally treated alumina.