Objective To evaluate the microtensile bond strength of three kinds of composite resins used as core materials around fiber posts with and without themocycling.Methods TENAX fiber posts were randomly divided into three groups,according to the resin composite used.They included one core materials specifically developed for core build-up ParaCore,one hybrid composite—AP-X,one flowable composite—Beautifil Flow.The fiber posts were then luted with a corresponding composite resin to be made into core-built up specimen.1 mm ×1 mm sticks were got from the specimen for microtensile testing with and without thermocycling.Results ParaCore,AP-X and Beautifil Flow with fiber posts decreased after thermocycling but there was no significant difference compared with which without thermocycling(P0.05).ParaCore with fiber posts was significantly higher than that of AP-X with and without thermocycling(P0.05).Conclusion 1)Within the limits of this study,thermocycling has no evident influence on three different resin composites.2)The bond performance of ParaCore is superior to the other two resin composites.