This paper describes the investigation of the individual effects of the introduced quantities of rare-earth elements (REE) and of SiO2/Al2O3 ratio on the physicochemical characteristics (textural properties and acidity) of Y zeolite, as well as on the catalytic activity of petrochemical cracking catalysts based on the zeolites prepared, during the conversion of hydrotreated vacuum gas oil (HTVGO). The amounts of REE oxides and the zeolite SiO2/Al2O3 ratio were quantified independently. An increase in REE oxide content in zeolite reduces its acidity. With an increase in SiO2/Al2O3 ratio at constant REE oxide content, the concentration of acid sites decreases, while the specific surface area and pore volume change only insignificantly. A growth in the REE2O3 content leads to a decline in the olefin yield from HTVGO cracking. Catalytic tests of the prepared catalysts demonstrated that an increase in SiO2/Al2O3 ratio enhances the C-2-C-4 olefin yield from HTVGO cracking as a result of the smaller contribution of hydrogen transfer reactions.