Mechanical activation (MA) is used extensively as a relatively no expensive method for the modification of physico-chemical properties of dispersed systems in technologies for obtaining powders and ceramics. Different processes that occur during MA of powders lead to the formation of specific structures that promote and accelerate solid-state reactions, as well as densification during sintering. Changes of particle size and structure during MA of the ceramic parent material are the sources of the morphological and structural metastability of the starting powders and they can affect the sintering process, positively or negatively. Many properties of final polycrystalline ceramics strongly depend on a green body microstructure and on conditions under which the green body is sintered. From the other side green body microstructure depend on a powders characteristics such as morphology, particle and pore size distributions. Regarding above mentioned activation and sintering must therefore be carried out under strictly controlled conditions in order to avoid influences that might cause a deterioration of the final properties of the ceramic materials. The present study is focused on the processes of sintering that occurred in mechanically activated single and multiphase oxide powders.