Synthesis of ceramics from silicon nitride nanopowders using hot-pressing and pressure-assisted and microwave (MW) sintering techniques has been studied. Dense ceramics with improved physicomechanical characteristics can be prepared on condition that most of the oxygen in the form of silicon monoxide (contained at 5 – 8 wt.% in the precursor powders) has been removed from the material. In ceramics treated by the three sintering technologies, an extensive grain growth is observed. The microstructure of these materials was more disperse in comparison with that of ceramic prepared from conventional α-Si3N4 powders synthesized in a furnace. This provides a route towards preparing nanopowder-based ceramics with a 25 – 30% increase in strength in comparison to ceramics of the same density prepared from conventional powders.