Inconel 690 is an austenitic nickel - based alloy, which has been used as a substitute material for Inconel 600 in steam generator (S/G) tubing in pressurized water reactor (PWR). In this study, the effects of heat treatment on fretting wear were investigated. From the microstructure observation, the solution annealing temperature and time had an influence on the grain size. The carbide morphology of Inconel 690 was mainly affected by the thermal treatment time and temperature. From the wear test results, it was shown that the larger grain size specimen wore less and cracks were found in carbides existing grain boundary except initial period of wear test of few carbide existing specimen. Cracks were not found in carbide free specimens. The hardness of specimen was not a major variable in fretting wear. Thus, it seemed that the carbides in grain boundary assisted crack formation and propagation in carbide existing specimens. It could be inferred that the critical mechanism of carbide existing specimen was delamination and that of carbide free specimen was abrasion. The larger grain size and carbides in grain boundary improved the wear property of Inconel 690 tube.