In this paper, ceria, CeO2, samples were prepared using three advanced synthesis methods: hydrothermal, sol-gel and mechanochemical synthesis. The prepared samples were characterized by X-ray diffraction analysis, thermogravimetric analysis, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorptiondesorption isotherms and diffuse reflection spectroscopy. It is shown that each of the three researched synthesis methods can be used to prepare nanocrystalline cerium (IV) oxide and that all three methods are suitable for the preparation of nanocrystalline cerium (IV) oxide doped with manganese. The sol-gel method enables the incorporation of manganese ions into the cerium (IV) oxide structure without presence of new phases, while in hydrothermally and mechanochemically derived samples, in addition to CeO2, birnessite, a phase with manganese also appears. The products of sol-gel and mechanochemical synthesis need to be subsequently thermally processed to obtain CeO2. However, if the products are intended for use in catalysis processes that occur at elevated temperatures, thermal treatment in necessary. The entry of manganese into the crystal structure of CeO2 was proven by the reduction of the unit cell parameter of the cubic crystal lattice of cerium (IV) oxide for the samples obtained by the three methods mentioned. A positive influence of manganese on the thermal stability of CeO2 was also observed, which is manifested in the smaller crystallite sizes of the doped samples compared to the non-doped ones. Although hydrothermal synthesis produced crystallites of the smallest size, sol-gel synthesis proved to be the method whose crystallites showed the smallest growth. Likewise, although the samples prepared by hydrothermal synthesis have the highest specific surfaces, after thermal treatment the samples prepared by sol-gel synthesis showed the highest surface area. One of the advantages of mechanochemical synthesis is obtaining the largest amount of product. The catalytic activity of the prepared samples was tested in the process of toluene or the aromatic (benzene, toluene, ethylbenzene and xylene, BTEX) gas mixture oxidation. All doped samples showed a significant increase in activity compared to non-doped ones. For each of the syntheses, doped samples achieved conversions of 95 % at a lower temperature compared to undoped samples, however, even the undoped sample prepared by sol-gel synthesis shows better catalytic activity than the most successful catalyst in the series obtained by mechanochemical synthesis. The increase in the catalytic activity of all samples in which part of the cerium is replaced by manganese is a consequence of the entry of ions of a lower oxidation state (Mn3+) instead of Ce4+ into the crystalline structure of CeO2. This results in the creation of oxygen vacancies and surface-active (unsaturated) sites that compensate for the negative charge. Also, doped samples are more thermally stable and have smaller particles and larger specific surfaces compared to non-doped ones.