Colloidal alumina was used to improve the activity of an In/HZSM-5 catalyst for the selective reduction of NO with CH 4 in the excess of oxygen. Compared with In/HZSM-5, the In/HZSM-5/Al 2 O 3 catalyst showed higher activity in a wide range of reaction temperatures. It is visualized that a synergetic effect between In/HZSM-5 and Al 2 O 3 enhances the conversion of NO x . The addition of Al 2 O 3 improved the conversion of NO to NO 2 and facilitated the activation of methane. An In/HZSM-5/Al 2 O 3 pre-treated with steam for 15h at 700 o C still showed a high activity for the removal of NO x with methane, while an In/HZSM-5 similarly pre-treated with steam showed a lower activity than the fresh sample. The activity of the In/HZSM-5/Al 2 O 3 catalyst could be restored completely after water vapor was removed from the feed gas. Furthermore, it was found that the In/HZSM-5/Al 2 O 3 remained fairly active under high GHSV and O 2 concentration conditions. It was also interesting to find that an increase in NO content could enhance the conversion of methane, and this illustrates that the existence of NO is beneficial for the activation of methane.