With increasing personalized healthcare, fiber-based wearable temperature sensors that can be incorporated into textiles have attracted more attention in the field of wearable electronics. Here, we present a flexible, well-passivated, polymer-nano-composite-based fiber temperature sensor fabricated by a thermal drawing process of multiple materials. We engineered a preform to optimize material processability and sensor performance by considering the rheological and functional proper-ties of the preform materials. The fiber temperature sensor consisted of a temperature-sensing core made from a conductive polymer composite of thermoplastic polylactic acid, a conductive carbon filler, reduced graphene oxide, and a highly flexible linear low-density polyethylene passivation layer. Our fiber temperature sensor exhibited adequate sensitivity (- 0.285%/degrees C) within a temperature range of 25-45 degrees C with rapid response and recovery times of 11.6 and 14.8 s, respectively. In addition, it demonstrated a consistent and reliable temperature response under repeated mechanical and chemical stresses, which satisfied the requirements for the long-term application of wearable fiber sensors. Furthermore, the fiber temperature sen-sor sewn onto a daily cloth and hand glove exhibited a highly stable performance in response to body temperature changes and temperature detection by touch. These results indicate the great potential of this sensor for applications in wearable, electronic skin, and other biomedical devices.