The effect of SO2 on catalytic activity for NO reduction to N-2 by methanol in excess oxygen over gamma-alumina has been investigated. SCR activity increased initially upon exposure of a fresh gamma-alumina catalyst to SO2 which is attributed to formation of Bronsted acid sites. Longer exposure to SO2 leads to a decline in catalytic activity to a lower steady-state NOx reduction activity which is independent of the SO2 content in the feed gas.