AbstractThe widespread application of flexible electronic devices places higher demands for stretchable conductors as crucial components owing to their stable and consistently high conductivity and high stretchability. In this study, a superelastic conductive fractal helix fiber (FHF) consisting of a thermoplastic polyurethane fiber and Ag wire is developed, which exhibits excellent waterproofing ability. The maximum strain of the FHF can be improved to 8300% by increasing the helical index C and Ag wire winding density. A high conductivity of 6.3 × 107 S m−1 and ultra‐high Q value of 3.37 × 104 at a strain of 5600% are realized for the conductive fiber owing to its fractal helical structure. The elastic limit point A of the FHF can be obtained by the relative resistance change (0.166%) to ensure that elastic deformation only occurs when stress is applied. In the elastic strain range, FHF demonstrates high electrical reliability under repeated deformation (over 10 000 cycles of stretching with a strain of 5600%) with a negligible increase in resistance. Moreover, the FHF can be easily integrated with the fabrics as an interconnection for wearable electronics. The newly developed twined FHF can also be used as a capacitive strain sensor to monitor human activity.