Characterization of the pyrolysis products of preceramic polysilazanes synthesized by reactions of the oligomer-[H2SiNMe]x in the presence of Ru3 (CO)12 catalyst has demonstrated that these polymers have great potential as precursors of Si3N4 for several applications. The polysilazanes studied are viscous liquids that can be converted to ceramic material with a yield of >65 wt %. The vitreous product contains regions of fully dense material and large cavities that indicate of considerable gas evolution. A preliminary pyrolysis sequence has been constructed based on a combination of TGA of the polymer, SEM investigation of the product, and mass spectroscopic analysis of the gases and heavy fragments released during conversion of the polysilazanes to ceramic material. This understanding of pyrolysis mechanisms will aid in developing even more effective polymeric precursors to Si3N4 and in optimizing pyrolysis procedures for a variety of useful appl ications.