The effects of alkali metal treatment on different zeolite catalysts are investigated to better understand the nature of alkali metal species for the selective catalytic alkylation of cumene by ethylene.H-ZSM5, Y and BEA zeolite catalysts with various molar ratios of K, Rb, and Cs are prepared by ion exchange method and calcined at 550 o C in air atmosphere for 2 h. The study was carried out at 300, 350, 400 and 450 °C for reaction times of 2 hours. Cumene conversion was found to increase with all different alkali metal additions and the reaction temperatures. The catalysts are characterized by temperature-programmed desorption of NH3/ or CO2 (TPD), Fourier transform infrared (FT-IR) after pyridine adsorption and inductively-coupled plasma emission spectrometry (i.c.p.e.s.). The FTIR results are compared to Lewis and Broensted acid sites. Furthermore, the relation between atomic size of alkali metal ion exchanged and the basicity of the catalyst is discussed. Among them the 0.025 M Cs exchanged is found as very active catalyst for alkylation of cumene with ethylene resulted in amyl benzene, styrene and ethyl benzene.