O-alkylation reaction of hydroquinone with excess methanol was performed by using alkali metal ionexchanged zeolite catalysts in a slurry type reactor to substitute the solid zeolite catalysts for the homogeneous liquid phase catalysts. This was also done to produce selectively mono-alkylated 4-methoxyphenol, a valuable intermediate for the perfume, flavor, food and photo industries. The effects of the basicity of various zeolites and reaction conditions such as temperature, reaction time and the amount of catalyst on the catalytic activity and selectivity were tested to maximize the yield of 4-methoxyphenol. Thus far, 84% selectivity at 95% conversion of hydroquinone was obtained at the optimum reaction conditions (240 ℃, reaction with 0.6 g catalyst for 16 h), which was thought to result from the strong basic property and shape selectivity of the Cs ion-exchanged NaX zeolite.