NiSe2 thermoelectric materials were prepared by the combination of mechanical alloying (MA) and spark plasma sintering (SPS). The effects of MA time and SPS temperature on the phase structure, microstructure, thermoelectric and optical properties were investigated. The results show that NiSe2 nanopowders with the grain sizes of 45 nm are synthesized by applying MA at 425 r/min for 40 h. It is proved that NiSe2 powder material is a direct band gap semiconductor with an optical band gap of about 2.653 eV and the NiSe2 bulk possesses a n-type semiconductive characteristic. The NiSe2 bulk prepared by applying SPS at 773 K attains a maximum power factor of 101 μW·m-1·K-2 along with a thermal conductivity 7.5 W·m-1·K-1 and the largest ZT value 0.0045