The effect of Pb²⁺ doping on the structure and thermoelectric properties of BiOCuSe (also known as BiCuSeO or BiCuOSe) is described. With increasing Pb²⁺ content, the expansion of the unit cell results in a weakening of the bonding between the [Bi_2(1−x)Pb_2xO₂]^2(1−x)+ and the [Cu₂Se₂]^2(1−x)− layers. The electrical resistivity and Seebeck coefficient decrease in a systematic way with growing Pb²⁺ levels. The thermal conductivity rises due to the increase of the electronic contribution with doping. The power factor of materials with a 4–5% Pb²⁺ content takes values of ca. 8 μW cm⁻¹ K⁻² over a wide temperature range. ZT at 673 K is enhanced by ca. 50% when compared to values found for other dopants, such as Sr²⁺ or Mg²⁺.