The production of propylene via a gas-phase metathesis of ethylene and 2-pentene has been studied over the Re2O7/SiO2-xAl(2)O catalysts containing various SiO2-Al2O3 compositions (13, 25, 50, 75, and 100 wt% Al2O3). Using ethylene and 2-pentene as the reactants, isomerization of the initial 1-butene product into 2-butenes and a subsequent secondary metathesis reaction between 2-butenes and excess ethylene enhanced the propylene formation so that propylene yield higher than its stoichiometric amount (> 50 %) could be obtained. While the pure Al2O3 supported Re2O7 catalyst possessed only the first type of isolated monomeric ReO4 (-) tetrahedra structure with a stronger Re-O-support bond, the second type with a weaker Re-O-support bond was observed on the SiO2-Al2O3 supported ones. The double-bond isomerization and the metathesis activities were optimized to produce the highest propylene yield over the Re2O7/SiO2-Al2O3 catalyst containing 50 wt% Al2O3. While the pure Al2O3 supported Re2O7 catalyst possessed only the first type of isolated monomeric ReO4 (-) tetrahedra structure with a stronger Re-O-support bond, the second type with a weaker Re-O-support bond was observed on the Re2O7/SiO2-Al2O3 catalysts and suggested to be the double-bond isomerization active sites. The isomerization of the initial 1-butene product into 2-butenes and a subsequent secondary metathesis reaction between these 2-butenes and excess ethylene resulted in the higher propylene yield. The optimum amount of alumina for the highest propylene yield was 50 wt%.