The study of cotransformation of petroleum fractions with vegetable oils on dual-zeolite cracking catalysts has revealed that vegetable oils differing in fatty acid composition admixed to vacuum gas oil, characterized by a high aromatics content, facilitate the conversion and increase the yields of the gasoline fraction and light olefins. In the case of vacuum gas oil cocracking with a vegetable oil having a high unsaturation index (sunflower oil), the oil content in the mixture should not exceed 5 wt %, since its higher content in the mixture leads to enhanced coking of the dual-zeolite catalyst and simultaneous reduction in the yield of the desired cracking products. The effect of preliminary impregnation of HREEY and HZSM-5 zeolites with ammonium hydrogen phosphate before their incorporation into the composition of dual-zeolite catalysts has been investigated as well. It has been found that the modification results in a decrease in the total acidity of zeolites. In the cracking of a mixture of vacuum gas oil and sunflower oil, it has been determined that the modification of zeolites leads to an increase in the total yield of the propane-propylene and butane-butylene fractions with high olefin content.