Acid sites located on the external surface of a MFI-type gallium-silicate crystals were selectively neutralized by a mechanochemical method using cerium oxide supported on spherical silica particles in micrometer size. The CeO2-modified catalyst exhibited longer catalyst life and higher yield of aromatics than a non-modified catalyst in an octane conversion reaction, and the coke deposited on a modified catalyst was much less than that on a non-modified one. This is attributed to that decrease in acid sites on the external surface of Ga-silicate crystals reduce the deep condensation of aromatic rings. The effect was further enhanced by the combination with Pt modification. The multifunctions of this catalyst are due to the aromatization ability of Ga species incorporated into the silicate framework, neutralization of external acid sites by CeO2 species, and dehydrogenation-cyclization of Pt particles on the external surface of crystals, respectively.