Te-doped CoSb3 was prepared by hot pressing and its doping effects on the thermoelectric properties were investigated. Single δ-phase was successfully obtained by encapsulated induction melting and the subsequent heat treatment at 773K for 24 hours, followed by hot pressing under 60 MPa at 773 K for 2 hours. Tellurium atoms successfully acted as electron donors by substituting antimony atoms and thermoelectric properties were remarkably improved by Te doping. Dimensionless figure of merit was obtained to be 0.80 at 650K for the CoSb2.9Te0.l specimen.