Dehalogenation copolymerization of 2,5-dibromothiophene and 2,5-dibromopyridine with zero-valent nickel complex gives random copolymers with molecular weight of 5x10(4)-5x10(6). They show unique doping-undoping cycles which are accounted for by shift of lone pair electron of pyridine ring to p-doped thiophene ring.