The modified H-ultrasil zeolite maintained high crystallinity and high specific surface areas precursors testified by XRD, BET and NH₃-TPD analysis. Effect of lanthanum concentration on the adsorptive, acidic and catalytic properties of H-ultrasil in the ethylbenzene ethylation reaction was investigated. Influence of modifying on catalytic properties of H-ultrasil zeolite is studied in a 300–400⁰C temperature interval. Under these conditions, selectivity of p-diethylbenzene in H-ultrasil is 42.1-44.4%. It is established that increasing concentration of lanthanum on H-ultrasil makes reduction of porous volume, essential decrease in concentration of the strong acid centers that in turn leads to increase selectivity on p-diethylbenzene. By the increase in concentration of lanthanum in H-ultrasil to 5.0 wt. % selectivity on p-diethylbenzene increases to 74.5%.