A Fe2VAl0.9Si0.1/Bi composite were fabricated using pulse-current sintering technique with mixed powder prepared by mechanical alloying. Since the raw powders were finely pulverized into nanometer sized crystallite and rapidly sintered to suppress grain growth during heat treatment, microstructural composite was obtained. The composite was consisted of Fe2VAl0.9Si0.1 grains with the size of 200-300 nm and nanometer-sized Bi particles. The size of the Bi particle decreased with the increase in the milling processing time, while the size of the Fe2VAl0.9Si0.1 grains showed no variation. The thermal conductivity of the composite decreased with the reduction of the Bi particle size, because of the increase in the number of hetero junction, at which phonons were scattered. On the contrary, the electrical conductivity was less affected by the incorporation of nanometer-sized Bi particles. This means that the hetero junction between Fe2VAl0.9Si0.1 and Bi has little effect on the carrier traveling or the dispersion of highly conductive Bi particles enhanced electrical conductivity. Although Seebeck coefficient was reduced by a negative effect of Bi incorporation on the Fe2VAl0.9Si0.1 crystal structure, the introduction of Bi nanoinclusions in the sintered Heusler material was effective to reduce the thermal conductivity without degradation of electrical conductivity and consequently improved the thermoelectric figure of merit.