The effect of steam treatment on HZSM-5 catalysts was analyzed during ethanol dehydration to ethylene. The parent and the steam treated HZSM-5 catalysts were characterized by various techniques. The results showed that the steam treatment created new mesopores on HZSM-5 zeolites by increasing the treatment temperature, which resulted in the coexistence of micropores and mesopores. The total amount of acid sites and the Bronsted/Lewis ratios of HZSM-5 zeolites decreased after steam treatment, especially for the strong acid sites. The steam treated catalyst at 500 degrees C (HT500) exhibited excellent catalytic stability and good selectivity for ethanol dehydration to ethylene. The improvement in the catalytic stability can be attributed to lower acidity, lower ratio of B/L and newly created mesopores after steam treatment. The analyses of the coke depositions over the spent catalysts indicated that the HT500 catalyst contained less coke deposition than that over the parent HZSM-5 did. The newly created mesopores on catalyst during the steam treatment may accommodate part of coke deposition, suppressing the formation of coke deposition in its inherent micropores to some extent. (C) 2012 Published by Elsevier B.V.