Aluminum-rich mesoporous aluminosilicate (Al-HMS) with a SUM ratio of 6.8 and a relatively narrow pore-size distribution was prepared from a 7:1 mixture of Si(OEt)(4) and AI(O-i-Pr)(3) via a sol-gel process. Compared with conventional porous aluminosilicates such as amorphous silica-alumina, commercial solid acid K10, dealuminated H-Y, and H-beta, the Al-HMS showed higher catalytic activity per aluminum atom for the Diels-Alder reaction between relatively unreactive dienophile alpha, beta-unsaturated esters with 1,3-dienes under very mild reaction conditions. Aluminum sites in the Al-HMS framework were found to behave effectively as solid acid, though the Al-HMS was relatively rich with aluminum. Al-HMS was also recyclable, and was comparable or superior to homogeneous Lewis acid AlCl3 in promoting the Diels-Alder reactions. Thanks to the possibility of safe handling of the Al-HMS and to its easy separation from organic products, Al-HMS becomes an alternative acid catalyst for the Diels-Alder reaction to homogeneous acids.