The reaction of polymerization of methylphenyldisilazanes and alkyl-phenyl-N-phenylaminosilanes under the action of alkalis at high temperature was studied. It was demonstrated that polymerization of the above compounds is accompanied by the evolution of benzene as a result of splitting off of phenyl groups from silicon atoms and of hydrogens from nitrogen atoms. When hydrogen atoms bound with nitrogen were exhausted, in the case of polymerization of symmetrical tetramethylphenyl-and dimethyl-tetraphenyldisilazanes, 1,1,3-trimethyl-1,3,3-triphenyldisilazane, and methyldiphenylphenylaminosilane, the reaction was kept going by the interaction of phenyls with the protons of the methyl groups. Polymers of a complex structure were obtained as a result.