Torsional fretting and torsional sliding wear behaviors of CuNiAl against 42CrMo4 were comparatively investigated in oil, filtered water and artificial seawater. Most experiment parameters except the angular displacement amplitude were set the same for all the tests. Compared with sliding tests, the averaged fretting friction torque of fretting tests tended to be higher but the wear rate was much lower, resulting from the influence of wear trace roughness, lubricant penetration behavior, surface strain hardening and third body effect. The fretting and sliding wear traces were mainly characterized by abrasion. The fretting wear traces under the filtered water and artificial seawater lubrications were also scattered with cracks and delamination, resulting from the frequent shear stress and poorer lubrication condition.