The Ag/alpha-Al2O3 catalyst modified with rare earth metal oxide (Y2O3) and alkali metal oxide (K2O) for the epoxidation of propylene by molecular oxygen were prepared and characterized by TG-DTA, XRD and XPS. The results show that a small quantity of Y2O3 added plays a role of electron and structure-type promoters, and can change the binding energies of Ag3d and restrain the sintering of Ag crystallites during catalyst preparation. The effects of promoters loading, Ag loading, reaction temperature, and calcination atmosphere on the performance of Ag catalyst were investigated. The results show that the loadings of K2O, Y2O3 and Ag, and reaction temperature affect obviously the catalytic performance of Ag-Y2O3-K2O/alpha-Al2O3 for the epoxidation of propylene to propylene oxide. Under the reaction conditions of 0.1 MPa, 245 degrees C, GHSV of 2000 h(-1) and the feed gas of 20%C3H6/8%O-2/N-2, the conversion of propylene of 4% and the selectivity to propylene oxide of 46.8% were achieved over the 20%Ag-0.1%Y2O3-0.1%K2O/alpha-Al2O3 catalyst.