Abstract: Selective synthesis of p-xylene by alkylation of toluene with dimethyl carbonate (DMC) was carried out in a continuous flow fixed-bed reactor over MgO-modified MCM-22 molecular sieves．The MgO/MCM-22 catalysts were characterized by means of XRD，N2 adsorption-desorption and pyridine-IR．Effects of MgO loading and reaction conditions were investigated．Results indicated that a high toluene conversion can be achieved along with an obvious increase in the selectivity for p-xylene over MgO modified MCM-22 using Mg(AC)2 as precursor．The influence of various reaction conditions was studied over a 12% MgO/MCM-22 catalyst．Under the optimal conditions，i.e. reaction temperature of 653 K，n (toluene) ：n (DMC) of 4 and WHSV of 1 h－1，the conversion of toluene and the selectivity to p-xylene were 31.01% and 55.61%，respectively．