In　order　to　select　appropriate　antifriction　and　wear　resistance　material　combinations　for　key　frictional　pairs　in　seawater　hydraulic　components,　tribological　characteristics　of　SiC,　Si3N4,　Al2O3,　and　ZrO2　ceramics　sliding　against　carbon　fiber/polytetrafluoroethylene/graphite-filled　polyetheretherketone　composite　lubricated　with　seawater　were　comparatively　investigated　with　a　ring-on-ring　test　rig.　The　results　show　that　the　nonoxide　ceramics　(Si3N4　and　SiC),　especially　the　Si3N4　ceramic,　exhibited　lower　friction　coefficients　and　smaller　wear　rates　than　those　of　oxide　ceramics　(Al2O3　and　ZrO2).　And　the　tribological　behaviors　of　polyetheretherketone/Si3N4　tribopair　under　dry　friction,　pure　water,　and　seawater　lubrications　are　further　comparatively　studied　to　explore　the　effect　of　lubricating　medium　on　the　tribological　characteristics　of　Si3N4　ceramic.　It　is　found　that　the　lubricating　effect　of　SiO2　and　Si(OH)(4)　films　generated　by　tribo-chemical　reaction　between　Si3N4　and　water　is　the　main　factor　for　the　relatively　low　friction　coefficient　and　wear　rate　of　polyetheretherketone/Si3N4　tribopair　under　aqueous　lubrication.　Under　seawater　lubrication,　the　Mg(OH)(2)　and　CaCO3　deposition　layers　caused　by　the　chemical　reaction　of　Mg2+　and　Ca2+　in　seawater　could　inhibit　the　generation　of　SiO2　and　Si(OH)(4)　films　and　increase　the　counterface　roughness.　As　a　result,　the　tribological　behaviors　of　polyetheretherketone/Si3N4　tribopair　are　worse　under　seawater　lubrication　than　that　of　pure　water　lubrication.