An oxide single crystalline whisker has been prepared which displays superior thermoelectric properties at high temperature in air. The whisker has an average composition of (Bi, Pb)2.2(Sr, Ca)2.8Co2Oy (abbreviated to BC-232 whisker) and a layered structure in which two different sublattices, CoO2 and rocksalt (Bi, Pb)2(Sr, Ca)2O4, alternate in the c-axis direction. Edge-sharing CoO2 layers act as conducting and thermoelectric units. Although a plateau is observed at around 500 K, the Seebeck coefficient of the whiskers is about 100 μV K−1 at 100 K, basically increases with temperature up to 773 K, and is saturated at temperatures higher than 773 K. Temperature dependence of electric resistivity shows semiconducting-like behavior but its value is very low compared with general semiconductors. These electrical phenomena would indicate pseudogap formation with its width of a few meV at the Fermi level. The power factor of the BC-232 whiskers is estimated at over 0.5 mWm−1 K−2 at temperatures higher than 650 K and reaches 0.9 mWm−1 K−2 at 973 K. © 2001 American Institute of Physics.