Amorphous silicon carbides are prepared by pyrolysis of a polycarbosilane precursor at different temperatures between 1000 degrees and 1400 degrees C. The structures of the resultant materials are analyzed using X-ray diffraction, electron paramagnetic resonance, and Raman spectroscopy. The optical properties of the SiC ceramics are investigated by measuring their absorption spectra. It is found that there is a critical temperature range, at which the structural and optical behavior varied in different ways as a function of pyrolysis temperature. The evolution in structures is discussed and the optical behavior is explained in terms of the structural evolution during pyrolysis at different temperatures.