Acid properties and catalytic activity of ultrastable zeolite Y modified with aqueous solutions of phosphoric and boric acid, as well as platinum-containing n-hexane hydroisomerization catalysts based on this zeolite, were studied. The modified specimens exhibited high activity in hydrocarbon conversion and selectivity for isohexanes. By using the method of regional rates, it was shown that there the catalyst activity and selectivity correlate with the number of acid sites with an activation energy of ammonia desorption of up to 120 kJ/mol.