The activities of Y-zeolite catalysts were studied in alkylation of toluene with methanol to produce xylene isomers. The experiments were carried out continuously over fixed bed catalysts and reactants wee fed by a micropump. The amount of total xylene decreased with time-on-stream, while the selectivity of p-xylene increased. In order to reduce the deactivation rate, catalysts were treated with water vapor or strong acids. It has been found that the modified catalysts by treatment show higher activities and lower deactivation rate than the corresponding untreated caltalysts. It has also been shown that the distribution of xylene isomers is dependent on the concentration of Brönsted acid of the catalysts employed. Moreover, the formation of m-xylene increased when the catalysts were treated with strong acids.