Single-component polymeric precursors to SiC/Si 3 N 4 /C/BN and Si 3 N 4 /BN ceramic nanocomposites were synthesized via hydroboration and dehydrocoupling of vinyl-containing cyclotrisilazanes. The polymer-to-ceramic conversion process was investigated by 13 C, 29 Si, and 11 B solid-state magic-angle spinning (MAS) NMR spectroscopy, FTIR spectroscopy, thermal analysis, elemental analysis, X-ray diffraction (XRD), and transmission electron microscopy. The yields, processibility, and resulting microstructure of the ceramics were dependent on the starting Si/B ratio in the polymers and the atmosphere used for pyrolysis. Thermal conversion of the polymers from 200 to 600 °C involved loss of vinyl functionality, an increase in the amount of B-N environments, and possibly some degradation of the silazane ring structure. Conversion of the polymeric environment to that of mixed-phase ceramic was complete between 600 and 1000 °C; XRD, however, showed the products to be amorphous even after heating to 1600 °C. Heating the N 2 pyrolyzed products to 1800 °C resulted in β-Si 3 N 4 , β-SiC, and t-BN peaks in the XRD powder patterns, while R-Si 3 N 4 and β-Si 3 N 4 peaks were observed for the NH 3 pyrolyzed products.