The layered oxyselenides BiCuSeO was recently discovered as potential thermoelectric. Our result reveals that the substitute for atom Bi3+ by Pb2+ & Mg2+ in (Bi2O2)(2-) play an important role in electrical transport properties. The maximum electrical conductivity obtained is 460Scm(-1) for Bi0.84Mg0.10Pb0.06CuSeO at RT, highly above the 15Sm(-1) for BiCuSeO. In synergy with low thermal conductivity (0.6-0.4Wm(-1)K(-1)) and large thermopower (300-500VK(-1)), the highest ZT is achieved about 0.80 at 873K for Bi0.88Mg0.06Pb0.06CuSeO.