Wide-gap ternary semiconductor CuIn5Se8 was prepared by the spark plasma sintering technique, and its thermoelectric properties were evaluated at 318~818 K. XRD analysis and band gap measurement indicate that this ternary compound is single phase CuIn5Se8 with its band gap of 1.13 eV, about 0.2 eV smaller than that of In2Se3. The magnitude of Seebeck coefficient decreases from 370.0 to 263.0 mV·K-1, and electrical conductivity increases from 1.44′102 to 2.92′103 W-1·m-1 with the temperature increasing. The thermal conductivity is 0.50 W·K-1·m-1, and the maximum thermoelectric figure of merit ZT is 0.33 at 818 K