Weldments in high-energy piping of fossil power plants are known to suffer extensive creep damage over the course of long-term operations. Repair welding after the removal of the deteriorated areas is considered as a potential method for improving the life of such weldments. Very few papers, however, are reported concerning the influence on creep rupture behaviour of repair welding performed at the end of the creep life of the weldments. In this paper, creep test of large weld specimens was carried out to create substantial numbers of creep voids, and these specimens were then repair-welded using various methods. On the basis of the results of subsequent creep rupture tests and stress analyses of these test specimens, the influence of repair welding on the creep rupture strength of deteriorated weldments was discussed.