Nitric acid treatment of CNTs-cordierite monolith changes the amount of Mg, Si, Al and oxygen-containing functional groups, thereby influencing on the surface area and pore size distribution of composite materials. Appropriate treatment of CNTs-cordierite with nitric acid increases the surface area and the amount of micropores slightly, but improves the activities for ammonia synthesis noticeable, which might be a consequent of the variation of the amount of Mg, Si, Al and oxygen-containing functional groups. The ammonia synthesis activity of Ba-Ru/CNTs-cordierite increase by more than 30% if the support material is treated at 30 degrees C for 4 h with nitric acid.