The fretting wear characteristics of STS304 steel in seawater were investigated experimentally. A fretting wear tester was designed to be suitable for this fretting test. This study was focused on the effects due to the combination of normal load, slip amplitude and number of cycles and corrosive environment as the main factors of fretting. The results of this study showed that the wear volume increased abruptly at slip amplitude between 70 $mu extrm{m}$∼100 $mu extrm{m}$ by fracture of oxide layers but above that slip amplitude the wear volume increased steadily.