Thermoelectric characteristics of a newly discovered commensurate ( q=0.5) misfit-layered oxide, [Bi 2Ba 1.8Co 0.2O 4± ω ] q CoO 2, have been significantly enhanced through partial Pb-for-Bi substitution: such substitution is found not only to reduce electrical resistivity and extend the temperature range for metallic conductivity, but also to raise the Seebeck coefficient. To obtain heavily Pb-substituted samples (up to 20–30% substitution level) requires careful control of both temperature and oxygen partial pressure during synthesis. Upon increasing Pb content, the lattice gets shrunken along the layer-piling ( c-axis) direction, while the q value remains constant at 0.5.