Polycrystalline AlMgB 14 and some hexaborides (CaB 6 , SrB 6 , YbB 6 , SmB 6 , and CeB 6 ) were synthesized to examine their thermoelectric properties. Single phase of orthorhombic AlMgB 14 , which contains B 12 icosahedral clusters as building blocks, was obtained at sintering temperatures between 1573 and 1823K. Seebeck coefficient (α) and electrical conductivity (σ) of the phase were about 500μV/K and 10 -1 1/Ω m at room temperature, respectively. These values are comparable to those of metal-doped β-rhombohedral boron. On the other hand, metal hexaborides with divalent cation possessed large negative α ranging from -100 to -270 μV/K at 1073K. Calculated power factors of CaB 6 and SrB 6 exceeded 10 -3 W/K 2 m within the entire range of temperature measured. As a result, they can be thought as promising candidates for n-type thermoelectric material.