In order to clarify the substitution effect of Nb for V on the thermoelectric properties of Heusler-type Fe 2VAl, we prepared the polycrystalline samples of Fe 2V 1− x Nb x Al ( x = 0, 0.05, 0.1, and 0.2) and the electrical resistivity ( ρ), Seebeck coefficient ( S), and thermal conductivity ( κ) were investigated. The samples with x = 0 and 0.05 were the Heusler-type single phase, while other samples contained a small amount of impurity phases. The Fe 2V 0.95Nb 0.05Al and the Fe 2V 0.9Nb 0.1Al samples as well as the Fe 2VAl sample exhibited relatively high power factor ( S 2 ρ −1) values (>10 −3 W m −1 K −2 at around room temperature), while that of the Fe 2V 0.8Nb 0.2Al sample was fairly low. The Nb-substituted Fe 2VAl samples indicated lower κ values than that of the Fe 2VAl sample, indicating that the effective phonon scattering due to the fluctuation effects between V and Nb occurred in the present system.