The thermoelectric properties such as the thermal conductivity, electrical resistivity and Seebeck coefficient of NaCo 2 O 4 and NaCo 1 . 9 M 0 . 1 O 4 (M=Ti, Rh, Pd) were evaluated in the temperature range from room temperature to 723 K. Polycrystalline samples were prepared by sintering in air followed by hot pressing. The thermal conductivity was calculated from the heat capacity, the experimental density, and the thermal diffusivity measured by the laser flash method. The electrical resistivity and Seebeck coefficient were measured simultaneously using ULVAC ZEM-1 in He atmosphere. The dimensionless figure of merit, ZT, of NaCo 1 . 9 Pd 0 . 1 O 4 was higher than that of NaCo 2 O 4 over a wide range of temperatures, and reached ZT=0.045 at 723 K.