The thermoelectric properties of AlMgB14-based materials prepared by spark plasma sintering were investigated. Al, Mg, and B powder were used as raw material powders. The raw powders were mixed using a V-shaped mixer, and then the mixture was sintered at 1673 K or 1773K. The mixture ratio of raw powders was varied around stoichiometric ratio of AlMgB14. X-ray diffraction patterns of samples showed that all samples consist of AlMgB14 and some by-products, MgAl2O4, B2O and AlB12. The Seebeck coefficient of the samples exhibited significant change depending on the varying mixture ratio. One sample exhibited a large negative value for the Seebeck coefficient (approximately -500 ��V/K) over the temperature range from 573K to 1073 K, while others showed positive value (250-450 ��V/K). Thus n-type AlMgB14-based material has been realized simply by varying raw material ratio.