The series LnMo8O14 (Ln = La, Ce, Pr, Nd and Sm) containing bicapped Mo8 clusters was synthesized via solid state reaction at 1673 K. Oxides of this type were reported to be narrow gap semiconductors. Our Seebeck coefficient measurements show that some of these reduced molybdenum oxides exhibit a thermopower of above −100 μV/K at room temperature, which is promising for the thermoelectric application. The highest power factor of 71 μW/mK2 was obtained for SmMo8O14 at 1152 K.