n-Type (Bi 2 Te 3 ) 0.9 –(Bi 2− x Cu x Se 3 ) 0.1 (x=0–0.2) alloys with Cu substitution for Bi were prepared by spark plasma-sintering technique and their structural and thermoelectric properties were evaluated. Rietveld analysis reveals that approximate 9.0% of Bi atomic sites are occupied by Cu atoms and less than 4.0wt% second phase Cu 2.86 Te 2 precipitated in the Cu-doped parent alloys. Measurements show that an introduction of a small amount of Cu (x⩽0.1) can reduce the lattice thermal conductivity (κ L ), and improve the electrical conductivity and Seebeck coefficient. An optimal dimensionless figure of merit (ZT) value of 0.98 is obtained for x=0.1 at 417K, which is obviously higher than those of Cu-free Bi 2 Se 0.3 Te 2.7 (ZT=0.66) and Ag-doped alloys (ZT=0.86) prepared by the same technologies.