The fretting wear test was carried at room temperature air and water to compare the wear properties of steam generator tube materials (Inconel 600 and 690) against ferritic stainless steels (405 and 409 stainless steel) and to understand the wear mechanisms at each test conditions. In room temperature air, the wear rate of tube materials increased with increasing normal loads and sliding amplitude. The results of SEM observation indicated that there are different mechanisms of wear particle removal and layer formation. The differences are related to the degree of adhesion force between wear particle and matrix due to the differences in chromium content in the tube materials. In room temperature water, the result indicated that the fretting wear rate and wear coefficient K in the work-rate model of Inconel 600MA were higher than those of Inconel 690TT with increasing normal loads and sliding amplitudes. From the results of SEM observation, there was little evidence of particle agglomeration on the worn surfaces, while wear particles were released in the form of thin plates, which were generated from deformation substructures formed by severe plastic deformation during fretting wear. Therefore, the wear rates of SG tube materials in the room temperature water are closely related with plastic deformation behavior on contact surfaces. In subsurface layer, wear particle size seems to be determined by cell-structure thickness and closely related to the difference of stacking fault energy of tube materials through chromium contents. Inconel 690 showed lower wear rate because it had lower stacking fault energy than Inconel 600 and well-developed smaller cells and in turn may easily accommodate large strains. Also, Inconel 600 and 690 have the critical thickness of plastic deformation layer. This means that wear rate in room temperature water is controlled by competition relationship between the removal of wear debris on the contact surface and crack nucleation and prop...