An In(4 wt%)-impregnated H-ZSM5 catalyst was characterized under wet and dry conditions by time-differential perturbed angular correlation (PAC) and by temperature-programmed reduction (TPR). Different indium species were quantified, correlating their structure with the catalyst deactivation due to the presence of water during the NO selective catalytic reduction (SCR) with methane. The fresh sample contains similar to60% of indium oxide and 40% of (InO)(+) species at exchange sites, the latter being the active species for the reaction under study. Under wet atmosphere, hyperfine interactions determined by PAC indicate the formation of two types of In hydroxide species and the decrease of both (InO)(+) and In2O3. TPR and PAC characterizations also show that deactivation is due to the decrease of (InO)(+) at exchange sites to form, after water is removed, different non-active In oxide species.