Conductive hydrogels are promising material candidates in artificial skin and muscles, flexible and implantable bioelectronics, and tissue engineering. However, it is still a challenging task to formulate hydrogels with high electrical conductivity without compromising their physicochemical properties. Herein, we report an interpenetrating poly(acrylic acid)-poly(3,4-ethylenedioxythiophene) (PAA-PEDOT) hydrogel with high electrical conductivity and good stretchability. A second PEDOT hydrogel network is electrochemically polymerized into an existing PAA hydrogel network. The interpenetrating hydrogel can be readily prepared and integrated into epidermal flexible electronic devices for the real-time, on-body detection of various ions in human sweat. The interpenetrating PAA-PEDOT conductive hydrogel has the potential to be an important building material for various flexible electronic devices for personalized healthcare.