The aim of the project is to develop high temperature resistant, relatively cheap material for use in oxidation atmosphere. This material can be used neat or as matrix of fiber composites. The pyrolysis of polymethylsiloxans and polyphenylsiloxans will b e used for preparation of these materials. For optimal choose of precursor and preparative conditions we need detail knowledge of pyrolysis process. Therefore changes structure and some characteristic properties of polysiloxanes during pyrolysis will be study, in dependence on exterior conditions and type of precursor. After estimation of experiment a model scheme will be proposed and corresponding kinetics. On base of acquired results will be proposed applicable thermal resistant materials and optimize d their preparation.