Preceramic perhydropolysilazane has been synthesized by the ammonolysis of dichlorosilane pyridine adduct. Perhydropolysilazane was polymerized and cross-linked by heat treatment with or without ammonia by dehydrogen condensation between SiH and NH and disproportionation at the SiH site in the polymers in the presence of pyridine. Ceramic yields of 82–93% were observed for perhydropolysilazane. The ceramic yield depended on the branching-group, i.e., −SiH < and −N<, content of the polymer. Controlled molecular weight distribution and elemental composition of the polymers obtained by heat treatment in the presence of pyridine meet various requirements for the production of shaped ceramics.