► Bi was successfully substituted for Sb in Cu3SbSe4. ► ZT for doped compounds was greater than that of un-doped Cu3SbSe4. ► In particular, ZT of Cu3Sb0.98Bi0.02Se4 reached a value of 0.7. ► Our results indicate Bi doping is an efficient way in improving TE properties. The thermoelectric properties of the bismuth doped compounds Cu3Sb1−xBixSe4, prepared by melting method and spark plasma sintering (SPS) technique, were investigated in the temperature range from 300K to 600K. The results indicate that the electrical resistivity of the Bi-doped compounds decreased as compare to Cu3SbSe4 due to the increase in the hole concentration; also thermal conductivity lowered after doping, which can be attributed to the strong phonons scattering by atom mass fluctuations. Moreover, it is found that the state of density effective mass m* increases for the doped compounds, which could be responsible for the enhanced thermopower at T>∼400K. The largest ZTmax=0.7 is achieved at 600K for Cu3Sb0.98Se0.02, which is about 3.3times larger than that of the un-doped compounds.