Light olefins and para-xylene were produced with high selectivity in the reaction of toluene with methanol over a modified HZSM-5 catalyst. Ordered mesoporous structure and weaker acidic sites led to significant contribution to the selectivity toward para-xylene. By means of a single-pulse reaction and the temperature-programmed surface reaction, it was confirmed that the presence of toluene and as-produced xylene shortened the reaction induction period and reduced the formation temperature of ethylene and propylene, which was beneficial to improve the selectivity toward light olefins, particularly ethylene.para-Xylene (PX) is one of the important organic materials used for the synthesis of pure terephthalic acid, which is used to make polyesters, particularly polyethylene terephathalate. In industrial processes, PX is produced from the aromatics of a naphtha catalytic reformer through complicated crystallization or adsorption separation; this method is very costly to obtain the desired purity of more than 99 %. The selective alkylation of toluene with methanol over the modified HZSM-5 catalyst has been studied extensively for decades. In general, steam treatment, [1] poison treatment of large molecules, [2] modification of Mg, [3,4] B, [5] P, [6] La, [7] Pt, [8] and so forth, and silylation method [9,10] were used to improve porous and acidic properties of the HZSM-5 catalyst to produce PX in concentrations greater than equilibrium concentrations. In addition, methanol reacted partially with toluene to produce alkylbenzenes and the rest was dehydrated to form hydrocarbons by using the methanol-to-hydrocarbon (MTH) process. [11] Some studies focused on improving the alkylation reaction as well as restraining side reactions. Thus, a high toluene/methanol molar feed ratio was often used, which would result in low conversion of toluene. However, light olefins, particularly ethylene and propylene, among hydrocarbons were not useless. They were important chemicals for the production of polyethy-lene and polypropylene, and ethylene was also a major component for the production of polyethylene terephathalate. Therefore, it would be meaningful to improve toluene conversion by using an optimum feed ratio of toluene and methanol, to restrain the formation of undesired aromatics with a designed catalyst, as well as to transform the excess methanol (unreacted with toluene) to important chemicals under the same conditions. Hence, we proposed a new mechanism to produce PX with use of extremely high-purity and high-concentration ethylene and propylene in one chemical reaction through the transformation of toluene and methanol (Scheme 1) over the modified HZSM-5 catalyst. It was also of great significance that the two materials used for the production of polyesters-PX and ethylene-could be obtained in one chemical reaction.The modified HZSM-5 catalyst for this process is expected to function in two transformations: one is the alkylation of toluene with methanol to produce PX with high selectivity and the other is the conversion ...