Cr- and Pt-promoted magnesium oxide catalysts were used to catalyze ortho-alkylation of phenol derivatives in the presence of excess methanol. The characteristic properties of the MgO surface measured by XRD, SEM, BET, and TPD suggest that Cr exists as fine chromium oxide particles on the MgO surface, while a Pt and MgO interaction causes an increase of the BET surface area as well as of surface acid and base amounts. Cr/MgO shows a specialty for ortho-alkylation of phenol derivatives with methanol without forming O-alkylated products, i.e.. anisole or methylated anisole. The catalytic activity and the stability of Cr/MgO are improved by the addition of a fairly small amount of Pt. The effect of Pt can be explained by the Pt and MgO interaction which increases both the acid and base amounts. A mechanism involving the reaction of phenol derivatives and methanol adsorbed simultaneously on acid-base pair sites is proposed.