The effects of preparation conditions, treatment methods of the Ag/TS-1 catalyst and the reaction conditions on propylene epoxidation using oxygen as the oxidant in a fixed-bed quartz reactor were investigated. The catalysts were characterized by XRD, UV-Vis, TEM and ESR spectra. Results show that hydrogen is essential for the epoxidation reaction. The optimum preparation conditions are as follows: Ag loading 2 wt.%, the ratio of Si/Ti in TS-164, and calcination temperature (in air) 450 degreesC. The optimum Ag/TS-1 catalyst, by passing a reactant mixture Of C3H6, O-2, H-2 and N-2 at 150 degreesC at a volume ratio of 1:2:3:12 with a space velocity of 4000 h(-1), can exhibit the best results. At this condition, after 70 min reaction the conversion of propylene and the selectivity to propylene oxide are 1.37 and 93.51%, respectively. The results of the characterization show that the oxidized Ag species without single electrons plays an important role in the epoxidation of propylene. (C) 2003 Elsevier B.V. All rights reserved.