The　thermal　expansion　properties,　dynamic　mechanical　properties,　and　related　tribological　properties　of　polyetheretherketone　(PEEK)　composites　filled　with　0-25　wt.%　content　of　calcium　carbonate　(CaCO3)　whisker　were　investigated.　The　composite　specimens　were　prepared　by　compression　moulding.　Thermomechanical　analysis　(TMA)　was　performed　to　determine　linear　coefficients　of　thermal　expansion　(CTE).　Dynamic　mechanical　thermo-analysis　(DMTA)　was　employed　within　the　temperature　range　of　25-300　°C.　Tribological　testing　of　composites　in　dry　wear　mode　against　a　carbon　steel　ring　was　carried　out　on　a　MM200　block-on-ring　apparatus.　All　specimens　show　a　large　change　in　CTE　at　glass　transition　temperature　(Tg),　but　CTEs　of　CaCO3/PEEK　composites　at　temperatures　below　and　above　Tg　are　much　lower　than　pure　PEEK.　For　25　per　cent　CaCO3/PEEK　the　average　CTE　in　the　temperature　range　of　25-120　°C　is　about　half　lower　than　PEEK.　CaCO　3　whisker　shows　a　significant　effect　on　the　dynamic　stiffness　at　low　and　high　temperatures.　The　increase　of　whisker　content　contributes　to　a　rise　to　the　storage　modulus.　CaCO3-whisker-filled　PEEK　composites　exhibit　considerably　lower　friction　coefficient　and　wear　rate　than　pure　PEEK.　With　an　increase　in　CaCO3　whisker　contents,　coefficient　of　friction　of　PEEK　composites　continuously　decreases,　while　the　specific　wear　rate　shows　minima　for　15　per　cent　CaCO3　whisker　inclusion　with　an　approximate　seven　times　improvement　in　comparison　with　PEEK.　The　improved　tribological　performance　of　CaCO3/PEEK　composites　is　ascribable　to　the　reinforcing　effectiveness　of　CaCO3　whisker,　which　contributes　to　increase　the　thermal　stability,　stiffness,　and　load-carrying　capacity　of　PEEK　composites　in　terms　of　counteracting　the　effects　of　thermal　softening　and　adhesion　during　the　friction　process.　©　2009　IMechE.