Side chain methylation of toluene and ethylbenzene using dimethylcarbonate has been studied at atmospheric pressure in the temperature range 673K–773K in a fixed bed reactor over Na, K and Cs exchanged X-type zoelite. Methylation of toluene produces ethylbenzene and i-propylbenzene as the main products while n-and i-propylbenzenes are the major alkylated products from ethylbenzene. The Cs exchanged sample, is the most active, the catalyst prepared by exchanging with alkali hydroxide being more active than that prepared from the chloride. The influences of process parameters such as duration of run, temperature and contact time on conversion and product yields have been investigated. Tentative mechanisms for the formation of the various products are proposed.