The object of this work is to study the effect of hydrothermal treatment on the TS-1/SiO2 catalyst in propylene epoxidation in fixed bed. The TS-1/SiO2 catalysts before and after hydrothermal treatment were characterized by means of XRD, XRF, BET, UV-Vis and EPR techniques. It was found by EPR characterization that two types of Ti(IV)-superoxide radicals, A (g(z) = 2.0271; g(y) = 2.0074; g(x) = 2.0010) and B (g(z) = 2.0247; g(y) = 2.0074; g(x) = 2.0010), were observed for the TS-1/SiO2 catalyst. The superoxo species A was converted to B after the TS-1/SiO2 catalyst was hydrothermally treated. The results show that hydrothermal treatment temperature and time have marked effects on the activity and the PO selectivity. The optimal hydrothermal treatment temperature and time are 170 and 4 h, respectively. In the long-term propylene epoxidation reaction, about 95% H2O2 conversion and above 94% PO selectivity are obtained over TS-1/SiO2 catalyst hydrothermally treated at 170 degreesC for 4 h.