Ca3-xAgxCo4O9+delta(x　=　0,　0.01,　0.03,　0.05)　oxide　samples　are　systematically　investigated　with　regard　to　their　phase　composition,　microstructure　and　thermoelectric　transport　properties.　The　results　show　that　all　oxide　samples　are　of　single　phase　and　they　have　layered　microstructure.　The　polarons　are　stabilized　by　Ag　doping　and　the　carrier　hopping　process　is　influenced;　the　electrical　resistivity　and　the　thermopower　are　found　to　be　increased　simultaneously.　The　electrical　performance　is　adjusted　and　the　Ca2.97Ag0.03Co4O9+delta　sample　possesses　optimum　power　factor,　the　total　thermal　conductivity　is　slightly　decreased　and　it　is　weakly　dependent　on　the　temperature.　These　results　suggest　that　doping　by　heavy　ions　within　low　concentration　would　be　an　effective　way　improving　thermoelectric　performance　of　Ca3Co4O9+delta　system.　(C)　2011　Elsevier　B.V.　All　rights　reserved.