Some studies have reported that alkaline treatment were effective in introducing mesoporosity especially in high-silicon zeolites, most favorably in dilute NaOH solution. This study was to optimize the alkaline treatment of mordenites and asses the feasibility of its combination to improve mordenite properties in term of high mesopores and high Si/Al ratio. Optimization of alkaline treatment of high Al mordenites was attained and the best results were obtained using a full hot demineralized water washing procedure. A combination of acid and alkaline treatments of mordenite was shown to give a high Si/Al ratio associated with mesoporosity and preserved or even improved crystallinity. The results of catalytic activity in benzene alkylation of samples exhibited a highly active catalyst with a good selectivity to diisopropyl benzene, low selectivity to triisopropyl benzene and n-propyl benzene, though less selectivity in cumene. The results of the study should be particularly useful to professionals, catalytic industries or anyone interested in research in material science.