The catalytic properties of zinc-modified, Ultrasil type high-silica zeolite in thermal catalytic conversion of gas condensate to produce olefins and aromatic hydrocarbons have been studied. Methods for controlling the product composition by varying zinc concentration and by steaming the modified zeolite have been proposed. It has been shown that the treatment of Zn-H-Ultrasil leads to the formation of Bronsted type weakly acidic OH group having an absorption band at 3670 cm(-1), which reduces the contribution of hydrogen redistribution reactions and enhances selectivity for lower C-2-C-4 olefins.