The effect of water on selective catalytic reduction of NOx using hydrocarbons (HG-SGR) on Cu- and Co-ZSM-5 was investigated. Co-ZSM-5 showed a higher HC-SCR activity and selectivity using C3H8 than Cu-ZSM-5 at temperatures above 400 degrees C in the presence of water. On Co-ZSM-5, C3H8 oxidation by O-2 was slow and severely inhibited by water due to Co-ZSM-5’s poor ability to adsorb O-2 dissociatively, and the capacity for NO adsorption was large enough to supplement the poor NO oxidation activity. These adsorption properties are therefore considered to contribute to the high activity and selectivity observed on Co-ZSM-5. Among the Go-based catalysts, Co-Beta showed higher HC-SCR activity and was more durable than Co-ZSM-5.