Te-doped CoSb3 was prepared by the encapsulated induction melting, and its doping effects on the thermoelectric properties were investigated. Single phase d-CoSb3 was successfully obtained by the subsequent annealing at 773K for 24 hours. Tellurium atoms acted as electron donors by substituting antimony atoms. Thermoelectric properties were remarkably improved by the appropriate doping. Dimensionless figure of merit was obtained to be 0.83 at 700K for the CoSb2.8Te0.2 specimen.