Silicon nitride based composites with different amount (1, 3 and 5 wt%) of carbon nanotubes have been prepared. Optimisation of the manufacturing processes has been conducted to preserve the carbon nanotubes in composites and to avoid damaging during high temperature processing. The first results show that carbon nanotubes have a good contact to the surface of silicon nitride grains. With increasing the carbon nanotube content a lower densification rate was obtained together with the deterioration of the mechanical characteristics of composites. In the case of 1wt% and 3 wt% carbon nanotube addition the increase of pressure resulted in increase of bending strength. It was found that microstructure features achieved by properly designed sintering parameters are the main responsible factors for the strength improvements.