Polyetheretherketone　(PEEK)　composite　specimens　filled　in　0-30　wt%　content　of　CaCO3　whisker　were　prepared　by　compression　moulding.　Tribological　testing　of　composites　was　carried　out　on　an　MM200　block-on-ring　apparatus　in　water　lubricated　wear　mode　against　carbon　steel.　The　morphologies　of　wear　traces　were　observed　by　scanning　electron　microscopy　(SEM).　The　effects　of　CaCO3　whisker　on　the　mechanical　and　tribological　properties　of　composites　were　investigated.　It　was　revealed　that　the　inclusion　of　CaCO3　whisker　significantly　improved　the　wear　resistance　and　reduced　the　friction　coefficient　of　PEEK　composites　under　water-lubricated　condition.　With　an　increase　in　CaCO3　whisker　contents,　the　friction　coefficient　decreased　and　showed　minima　for　15　per　cent　CaCO3　inclusion.　The　specific　wear　rate　of　composites　showed　minima　as　2.04　x　10(-6)　mm(3)/Nm　for　20　per　cent　CaCO3　inclusion　as　5.2　per　cent　of　that　for　pure　PEEK,　followed　by　a　slow　increase　for　further　CaCO3　whisker　addition.　In　terms　of　friction　applications　under　water　lubrication,　when　the　tribological　and　mechanical　properties　were　combined,　the　optimal　content　of　CaCO3　whisker　in　the　filled　PEEK　should　be　recommended　as　15-20　per　cent.　The　SEM　observation　of　the　wear　traces　indicated　that　CaCO3　whisker　contributed　to　increase　the　load-carrying　capacity　and　abate　the　scuffing　and　adhesion　of　filled　composites,　which　conformed　to　the　better　wear　resistance　of　CaCO3/PEEK　composites　than　pure　PEEK.　No　transfer　film　could　be　observed　on　the　counterface　of　the　mating　ring　under　water-lubricated　condition.　It　is　confirmed　that　the　transfer　film　is　not　the　main　reason　for　the　enhancement　of　wear　resistance　of　the　composites　in　water　lubrication.