The Seebeck coefficient in the ternary system (Fe,V)3Al with D03 structure was measured. It increased modestly with 0-20 mol%V replacement. A large increase for 20-25 mol%V replacement and a subsequent sharp drop to a negative value was found at room temperature. The maximum and the minimum value were +75 microV/K and -165 microV/K at Fe-23 mol%V-25 mol%Al and at Fe-27 mol%V-25 mol%Al, respectively. These values were better than the reported values in the Fe-based thermoelectric materials, but became smaller at higher temperatures. The compositional dependency of the Seebeck coefficient reflects the density of state at the Fermi level, because V atoms selectively replace Fe atoms in the ordered D03 crystal lattice.