Selective catalytic reduction of NO with propene was investigated over In2O3/Al2O3 catalysts prepared by three methods, namely, a single sol-gel (SG), impregnation (IM), and co-precipitation method (CP). The catalysts were characterized by means of BET, XRD, XPS, and TPD. The maximum NO conversion over In2O3/Al-2 O-3 prepared by sol-gel method was 95% at 400 degrees C in the absence of H2O, and the activity decreased slightly in the presence of H2O, and it was still 76% even in the presence of H2O and SO2. Although the retarding effect of SO2 on the activity was observed for the three catalysts, In2O3/Al2O3 (SG) showed relatively high activity. It is found that the high surface area and low average pore diameter are important to the catalytic activity, and the strong interaction between indium and alumina for In2O3/Al2O3 catalyst prepared by sol-gel method may be the reason of high activity for NO reduction. The reaction and surface studies showed that NO3- and partially oxidized hydrocarbons (RCOO- species) are mainly intermediates, and the oxidation C3H6 to RCOO- species maybe the key reaction process in the SCR of NO with C3H6.