P- and N-type thermoelectric iron oxides were developed. The p- and n-type thermoelectric iron oxides were based on delafossite-type CuFeO2 and spinel-type Fe3O4, respectively. The dimensionless figure of merit, ZT, of the bulk p- and n-type iron oxides were 0.15 and 0.10 at 1200K, respectively. The ZT values were improved by the introduction of nano-voids. The physical properties of these iron oxides are structurally unique because of the triangular, or “Kagome,” arrangement of FeO6 octahedra. The delafossite-type CuFeO2 becomes anti-ferromagnet at temperatures less than 20K. The inverse spinel-type Fe3O4 is a ferrimagnet at room temperature. In both crystals, the iron ions are assumed to be in the high-spin state.