Silicon nitride based composites with 3wt% of single wall carbon nanotubes and exfoliated graphite have been prepared. Optimisation of the manufacturing processes has been conducted to preserve the carbon nanotubes and exfoliated graphite in composites and to avoid damaging during high temperature processing. The first results show that carbon nanotubes and exfoliated graphite have a good contact to the surface of silicon nitride grains. In the case of increase of sintering pressure an increase of bending strength was achieved. It was found that microstructure features achieved by properly designed sintering parameters are the main responsible factors for the strength improvements.