Results are presented of investigations of the porous structure of the Al2O3-La2O3 systems containing up to 10 wt% of the La modifying oxide prepared by the coprecipitation method. Pore size distribution was determined on the basis of low temperature nitrogen adsorption measurements and mercury intrusion porosimetry. The changes in pore size distribution of different forms of Al2O3-La2O3 are discussed in relation to the concentration of the lanthanum oxide.