The conversion of methanol was carried out over various mordenite zeolite catalysts to evaluate their catalytic performance. A post-preparation treatment of the H-MOR catalyst by halogenation with NH4Cl or NH4F and by hydrohalogenation with HCl or HF was carried out and its effect on methanol conversion reactions at 100-300 ℃ in a continuous flow reactor was investigated. The as-synthesized H-mordenite (H-MOR) is generally more active during dimethyl ether (DME) production than the NH4-MOR and Na-MOR. Fluorinated treatment with HF or NH4F significantly improved the catalytic activity during methanol conversion and the formation of DME in comparison to chlorinated treatments with HCl or NH4Cl. This is principally attributed to the higher Si/Al ratio and an increase in the number of acid sites and their strength. Halogenation treatment with the acids of both F- or Cl- gave the highest conversion activity for DME production compared to halogenation treatments with the salts of the same halogens. Zeolite dealumination by the acids was more profound than that by the halogen ion salts, which resulted in a decrease in the crystallinity and crystallite sizes of the zeolite.