We investigated the thermoelectric properties of an In4Se3− x Cl y /BaIn2Se4 composite. In spite of a phase separation with the large-bandgap material BaIn2Se4 in the In4Se3− x Cl y matrix, the electrical resistivity of the In4Se3− x Cl y /BaIn2Se4 composite was significantly decreased compared to that of the pristine compound of In4Se2.7Cl0.03 due to the increased Hall mobility of the carriers. The Seebeck coefficient and thermal conductivity did not change significantly, whereas the electrical resistivity decreased for the composite, resulting in an enhancement of the power factor and the ZT value in a mid-temperature range (below 565 K).