The conversion of an ethylene-pentane mixture over HZSM-5 zeolite (Si/Al = 35) modified with molybdenum and boron has been studied. The texture, dispersion, and structure of the catalyst have been determined by instrumental methods. The modification with molybdenum leads to an increase in both the activity of the catalyst in the conversion of the ethylene-pentane mixture and the yield of C-5-C-9 isoparaffins and aromatic hydrocarbons with high octane numbers. The ratio of isoparaffins and aromatic hydrocarbons in the products on the catalyst that contains molybdenum and boron depends upon the reaction conditions. DOI: 10.1134/S096554411206014X