Changes induced in the structure of ultrastable zeolite Y by its modification with aqueous solutions of phosphoric and boric acids were studied using the techniques of scanning microscopy, X-ray diffraction, X-ray emission analysis, and IR spectroscopy. The data obtained were compared with the results of measurements of benzene and cyclohexane adsorption on the same specimens. It was shown that the application of modifiers does not lead to the formation of new phases. The specimens also did not undergo additional dealumination, although the treatments attempted somewhat decreased their crystallinity. The introduction of progressively increasing amounts of boric acid or the combined treatment with phosphorus and boron compounds favors a marked decrease in the adsorption ability with respect to cyclic C-6 hydrocarbons.