The methylation of cyclopentadiene with methanol has been studied over Al2O3 and KOH promoted MgO and unpromoted MgO. The dehydrogenation of methanol to formaldehyde was found to be a key-step in the generation of the active methylating species on these solid bases. The modification with Al2O3 or KOH favors the formation of methylcyclopentadienes and elevates the activity of MgO based on different reasons: introduction of acidic sites for Al2O3/MgO and superbasic effect for KOH/MgO. These catalysts present different deactivation behaviors due to the different surface acid-base properties. The heavy coking of cyclopentadiene on basic sites is responsible for the rapid deactivation of KOH/MgO along the catalytic test at 773 K. However, the coking can be well suppressed at 723 K, and KOH/MgO exhibits the catalytic performance apparently superior to MgO and Al2O3/MgO. (C) 2010 Elsevier Inc. All rights reserved.