Creep tests and microstructural observations in several high Cr ferritic steels bearing V and Nb were carried out in order to investigate effects of addition of V and Nb on , which is a coefficient of method. Creep strength was improved with increasing the V content and was slightly lowered by increasing the Nb content. in all the steels bearing V or Nb was lager than that in fundamental steel. The dependence of on the amount of additions was different between V and Nb. In steels bearing V, became larger with increasing V content. In steels bearing Nb, became smaller. These results revealed that corresponds to the creep strength, indicating that the value of can be estimated using the strengthening effects of the additive element.