New pyropolymers of the form of a tough film with a good electrical conductivity have been developed by carbonization of poly(α-chloroacrylonitrile) and polycarbodiimide. To elucidate the electrical conduction mechanism in conjunction with a formation of conjugated structure upon carbonization, we have made measurements of proton NMR relaxation rate (T 1 −1) as a function of the NMR frequency between 4–300 MHz as well as the conventional and the VSC (voltage-shorted-compaction) conductivity measurement between 1–300K. Changes in molecular structure from 1d to 2d and from 2d to 3d by proceeding the carbonization were demonstrated through the changes in the frequency dependence of T 1 −1. Temperature dependence of the electrical conductivity is as a whole of semiconductor type and yet a metallic temperature dependence was obtained by the VSC measurement, showing the existence of metal-like regions.