Preceramic polymer of Si-N(-C), perhydro-polysilazane (PHS), polyborosilazane (PBS) and methyl-hydropolysilazane (MHS), were synthesized by a pyridine-adduct method. The properties of polysilazanes were examined in relation to their potential application to the precursors of ceramic composites. PBS had too high viscosity to be impregnated in a fibrous preform. Accordingly, a mixture of PBS and PHS with the mass ratio of PBS/PHS=1/10 (PHS-B) was studied as the alternative of PBS. The char-yield of the respective raw polymers ranged from 60 to 80mass%, while that of the cured polymers was by 10-20mass% higher than the raw polymers. The polymers pyrolyzed below 1400K were amorphous. However, α-Si3N4 crystallites were observed at higher temperatures exceeding 1473K for PHS, 1673K for PHS-B and 1723K for MHS. The crystallization increased the density from 2.4Mg/m3 to 3.1Mg/m3 at the maximum. The MHS pyrolyzed at 1723K, being nearly amorphous, the heat-resistance of which was examined in nitrogen atmosphere for the exposing time span of 360ks. The heat-resistance test at 1723K significantly enhanced the crystallization, the test at 1623K resulted in a subtle change in crystallization, and the test at 1523K caused no microstructural change. It was concluded from these heat-resistance test results that the amorphous Si-N-C via MHS may be usable as a matrix of ceramic composites at temperatures below 1623K.