Impregnation of FAU zeolites with seven cesium hydroxide atoms per unit cell improved their basic properties in toluene methylation without affecting the physical properties of the zeolite (framework, silicon/aluminium molar ratio, aluminium coordination, etc.). The enhancement was greater in the zeolites with good initial basic properties such as the cesium-exchanged zeolite. The effect of the impregnation was to first decrease the acid activity and then to increase the basic activity. The basic catalytic activity showed a maximum for a cesium content of 20CsOH/u.c. in the NaX zeolite. Higher contents of cesium hydroxide did not show catalytic activity due to the collapse of the FAU framework. Higher yields of basic methylation were achieved with a zeolite synthesised with occluded alkaline hydroxide (NaKX-I) without post-synthesis treatment. In this case, the cesium hydroxide content yielding the maximum catalytic activity was 15CsOH/u.c.