Highly stretchable and conductive core鈥搒heath nanofibers are significant for flexible and wearable microelectronics. Core鈥搒heath fibers were massively fabricated from ultralong chemical vapor deposition (CVD)-grown graphene bundles. They exhibited superior conductivity and excellent mechanical properties that exceeded those of the reduced graphene oxide fibers. The intrinsic dynamic fracture procedure and mechanism of the core鈥搒heath nanofibers were investigated. Furthermore, safe strain sensors based on as-prepared core鈥搒heath CVD graphene fibers have been demonstrated as a proof-of-concept application. The performance of strain sensors has been greatly improved by using CVD graphene fibers.