The results of measurements of the optical absorption spectra, IR absorption spectra, thermogravimetric analysis, and elementary analysis of pyrolyzed polyacrilonitrile are presented as a function of the pyrolysis temperature Tp and of the duration of pyrolysis. At Tp ∼ 200°C, an intermediate phase was discovered, containing conjugated CN sequences and a completely unreacted carbon backbone. The optical absorption data imply that the resulting polymer is a semiconductor with a delocalized π-electron system and an energy gap Eg ⋍ 2.5 eV. For Tp > 260°C, the weight loss rapidly increases, and the absorption edge gradually broadens and shifts to lower energies. The resulting polymer (after higher-temperature pyrolysis) contains CN and C[DOUBLE BOND]C[BOND]C conjugation sequences, but appears to be a complex structure consisting of a mixture of different chemical species.