It was shown that the concentration of the modifier (manganese ions (II)) significantly affects the structural properties of the modified aluminum oxyhydroxide. In the phase composition of the samples modified and reduced content hydroxid and oxyhydroxide aluminum phases, which leads to a drop of the specific surface area from 196,16 to 10,78 m2/g. In the modified heating samples in air joint formed of aluminum oxide and manganese phase - MnAl2O4, and in the sample with the highest content of manganese oxides, manganese own found - Mn3O4, Mn2O3. The presence of manganese oxide phases making a modified aluminum oxyhydroxide promising as a catalyst for the oxidation of organic and inorganic compounds