PHENOL, CRESOL OR THE LIKE PHENOLS EACH HAVING AT LEAST ONE HYDROGEN ATOM AT ORTHO-POSITION, IS METHYLATED AT ORTHO-POSITION THEREOF IN HIGH SELECTIVITY BY REACTING WITH METHANOL USING A NOVEL CATALYST SYSTEM SELECTED FROM THE LEAST ONE OF THE FOLLOWING GROUPS (A), (B) AND (C): (A) A COMBINATION OF AT LEAST ONE OF MAGNESIUM OXIDE, ZINC OXIDE AND BERYLLIUM OXIDE, AT LEAST ONE OF LATHANIDE OXIDE, SCANDIUM OXIDE AND YTTRIUM OXIDE, AND AT LEAST ONE OF URANIUM OXIDE AND TIN OXIDE; (B) A COMBINATION OF AT LEAST ONE OF SCANDIUM OXIDE, YTTRIUM OXIDE AND LANTHANIDE OXIDE, AND TIN OXIDE; AND (C) A COMBINATION OF AT LEAST ONE OF URANIUM OXIDE AND LANTHANIDE OXIDE, AND ACTIVE CARBON.