Selective catalytic reduction of NO with propene was investigated over In 2 O 3 /Al 2 O 3 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 In 2 O 3 /Al 2 O 3 prepared by sol-gel method was 95% at 400°C in the absence of H 2 O, and the activity decreased slightly in the presence of H 2 O, and it was still 76% even in the presence of H 2 O and SO 2 . Although the retarding effect of SO 2 on the activity was observed for the three catalysts, In 2 O 3 /Al 2 O 3 (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 In 2 O 3 /Al 2 O 3 catalyst prepared by sol-gel method may be the reason of high activity for NO reduction. The reaction and surface studies showed that NO 3 ) and partially oxidized hydrocarbons (RCOO ) species) are mainly intermediates, and the oxidation C 3 H 6 to RCOO ) species maybe the key reaction process in the SCR of NO with C 3 H 6 .