The effects of calcination atmosphere of the Ag/TS-1 catalyst and other Ti-containing supports on propylene epoxidation using oxygen as the oxidant in a fixed-bed quartz reactor were investigated. The samples were characterized by XRD, UV vis, ESR, TEM and FT-IR. The results show that 2 wt.% Ag/TS-1 calcined in air is optimum; the Ag/Ti-containing (prepared by chemical vapor deposition (CVD) or impregnation (IMP) method) catalysts have catalytic activities in the reaction. The framework titanium species plays an important role, while the extra framework titanium species (280-290 nm) also has weak epoxidation activity in the gas-phase epoxidation of propylene; excessive extra framework titanium species (280-290 nm) can decrease PO selectivity. The oxidized silver ions are the main active sites for the gas-phase epoxidation of propylene. (C) 2004 Elsevier B.V. All rights reserved.