The transalkylation reaction between mesitylene and naphthalene has been studied over pentasil zeolites, type H-ZSM-11. The main product was 2-methylnaphthalene. The influence of external and total surface area of the catalysts on catalytic activity and selectivity was investigated. From these observations, it was found that the external surface of zeolites played a key role in the synthesis of 2-methylnaphthalene.