Alkylation of toluene with Propylene over HZSM-5 pellets and HZSM-5 pellets modified by the chemical liquid deposition of SiCl4 was performed in this study. The modification was made by adding a mixture of SiCl4 and hexane to the parent HZSM-5 pellets containing 14% of water. Under the most appropriate operating conditions for alkylation, which were a temperature of 523 K, a weight hourly space velocity of 4.6 (g of toluene)/(g of catalyst)/h, and a molar ratio of toluene to propylene of 7.7, the p-cymene selectivity and yield obtained using the modified HZSM-5 pellets were much higher than those obtained using the parent ones. The experimental data indicate not only that the p-cymene selectivity could exceed 90% as it increased with time during a sixty-hour run using the modified pellets, but also that the yield increased as the reaction proceeded.