Poly(ethylene　terephthalate)　(PET)　composites　containing　carbon　fiber　(CF)　or　polymethyl　methacrylate　(PMMA)-grafted　carbon　fiber　(PMMA-g-CF)　were　prepared　by　melt　compounding.　The　rheology,　non-isothermal　crystallization　behavior,　and　mechanical　and　thermal　properties　of　pure　PET,　PET/CF　and　PET/PMMA-g-CF　composites　were　investigated.　The　results　show　that　the　addition　of　CF　or　PMMA-g-CF　significantly　increases　the　storage　modulus　(G＇),　loss　modulus　(G＇＇),　and　complex　viscosity　(η*)　of　the　composites　at　low　frequency.　The　Cole-Cole　plots　confirm　that　the　surface　modification　of　CF　leads　to　a　better　interaction　between　the　CF　and　PET,　and　then　decreases　the　heterogeneity　of　the　polymeric　systems,　which　is　confirmed　by　the　SEM　observation　on　the　tensile　fracture　surface　of　the　composites.　Non-isothermal　crystallization　analysis　shows　that　the　CF　or　PMMA-g-CF　could　serve　as　nucleation　agent　to　accelerate　the　crystallization　rate　of　the　composites,　and　the　effect　of　PMMA-g-CF　is　stronger　than　that　of　CF.　The　result　is　further　confirmed　by　the　analysis　of　the　crystallization　activation　energy　for　all　composites　calculated　by　the　Flynn-Wall-Ozawa　method.　Moreover,　the　tensile　and　impact　strength　and　the　thermal　stability　of　the　composites　are　improved　by　CF,　while　the　incorporation　of　PMMA-g-CF　further　enhances　the　tensile　and　impact　strength　and　thermal　stability.　©　2018　by　the　authors.