Strain sensors based on percolated networks of poly(3,4-ethylenedioxythiophene) (PEDOT) in thermoplastic polyurethane (TPU) matrix fabricated through in situ vapor phase polymerization (VPP) is reported. The hybrid made of elastomer and conductive polymer shows uniform PEDOT distribution on the surface and inner side of the TPU due to the effective penetration, diffusion, and polymerization of EDOT. Performance of sensors using two kinds of oxidants (FeCl3 or iron(III) ptoluenesulfonate( FTS)) are compared and the concentration is varied to obtain the best electromechanical properties. Amount of PEDOT increases with increasing amount of oxidant: thereby improving the electrical conductivity, while the elasticity of the hybrid decreases. The elasticity reduction phenomenon is diminished when FTS is used due to the plasticizer effect of the tosylate ion on the TPU. The performances of PEDOT.TPU hybrids prepared with FTS are excellent in the terms of stretchability (>300%), gauge factor (GF > 10 @ strain 100%), resistance variation reproducibility under various strain modes, small hysteresis, and durability (>1000 cycle). With the electromechanical performance, as well as cheap and scalable production, the PEDOT/TPU sensor holds tremendous prospects on flexible and stretchable devices for human motion monitoring, as well as present strategies on architecture of conductive soft materials.