In-filled and Te-doped CoSb3 skutterudites were prepared by encapsulated induction melting, and their thermoelectric properties were investigated from 300 to 700 K. Single 8-phase was successfully obtained by the subsequent heat treatment at 823 K for 5 days. In-filled and Te-doped InzCO4Sb12-yTey showed the n-type conduction at all temperatures examined, indicating that Te atoms successfully acted as electron donors by substituting Sb atoms. Electrical resistivity was reduced by In filling and Te doping, and the Te doping effect on the resistivity decrease was predominant. Thermal conductivity was considerably reduced by In filling as well as Te doping due to the increase in phonon scattering, which shows that the lattice thermal conductivity is much larger than the electronic thermal conductivity in the InzCo4Sb12-yTey systems. (C) 2007 Elsevier B.V. All rights reserved.