The effect of micro- and nano-sized CeO2 powder additives on acidic and catalytic properties of MFI (mordenite-framework-inverted) type of high-silicon zeolite in the process of production of high-octane motor fuel components from straight-run gasolines of gas condensate is studied. Addition of modifying agents to the original zeolite promotes its catalytic activity and concentration of acid centers. Addition of 1 wt. % of promoting additives of nano-sized CeO2 powder to zeolite enhances yield of arenes in the liquid catalyzate by 4-7 wt. % and octane number (ON) of the obtained catalyzate by 2-3 points in terms of RON. It is shown that zeolite modified by micro-sized CeO2 powder possesses similar catalytic and acidic properties as does zeolite modified by nano-sized CeO2 powder.