The present invention relates to a novel oxide catalyst, more specifically, a novel modified magnesium oxide catalyst which is highly active and selective for ortho-alkylation of phenol.The catalysts for phenol alkylation of the invention are represented as Mg.sub.a Mn.sub.b L.sub.c T.sub.d Q.sub.e O.sub.x .wherein:L is vanadium or chromium;T is alkali metal, alkali earth metal, lead, bisumth, cobalt, aluminum, silicon., gallium, germanium or molybdenum;Q is antimony, cesium or iron;b/a=0 to 0.35(atomic molar ratio);c/a=0.01 to 0.35(atomic molar ratio);d/a=0 to 0.35(atomic molar ratio);e/c=0.1 to 10(atomic molar ratio); and,x is determined by oxidation state of each component.