Abstract The Fe(II) or Fe(III) complex and the Fe(II)/Fe(III) mixed-valence complexes of o, o'-dihydroxyazobenzene (DHA) were prepared by mixing DHA with methanolic solutions containing FeCl 2 and FeCl 3 in various molar ratios. The maximum conductivity value of the resulting coordination polymer was obtained when the molar ratio Fe(II):Fe(III) was 0.2:0.8. This suggests that charge carriers are created on the polymeric linkage by changing the oxidation states of some of the metal centers. When the pellets of the Fe(II)/Fe(III) mixed-valence polymers were exposed to I 2 vapor, the conductivity decreased initially and then increased. The biphasic change is attributed to the initial oxidation of Fe(II) ions to Fe(III) ions and by the subsequent oxidation of the organic moieties of the polymer. Thus, the mixed-valence metal centers connected by azo linkages appear to behave as the conduction pathway in the novel intrinsically semiconducting polymers.