Conductive polymers are recognized as ideal candidates for the development of noninvasive and wearable sensors for real‐time monitoring of potassium ions (K+) in sweat to ensure the health of life. However, the low ion‐to‐electron transduction efficiency and limited active surface area hamper the development of high‐performance sensors for low‐concentration K+ detection in the sweat. Herein, a wearable K+ sensor is developed by tailoring the nanostructure of polypyrrole (PPy), serving as an ion‐to‐electron transduction layer, for accurately and stably tracing the K+ fluctuation in human sweat. The PPy nanostructures can be tailored from nanospheres to nanofibers by controlling the supramolecular assembly process during PPy polymerization. Resultantly, the ion‐to‐electron transduction efficiency (17‐fold increase in conductivity) and active surface area (1.3‐fold enhancement) are significantly enhanced, accompanied by minimized water layer formation. The optimal PPy nanofibers‐based K+ sensor achieved a high sensitivity of 62 mV decade−1, good selectivity, and solid stability. After being integrated with a temperature sensor, the manufactured wearable sensor realized accurate monitoring of K+ fluctuation in the human sweat. The polypyrrole (PPy) nanostructures are tailored from nanospheres to nanofibers via controlling the supramolecular assembly process, which is utilized as the ion‐to‐electron conductive layer. Resultantly, the ion‐to‐electron transduction efficiency and active surface area are significantly enhanced, accompanied by minimized water layer formation. The optimal PPy nanofiber‐based potassium ion (K+) sensor achieved a high sensitivity of 62 mV decade−1, good selectivity, and solid stability.