The combination of conductive material and flexible material is an unavoidable problem in the preparation of flexible sensor, but uniform combination of the materials in micro- or nanostructure is difficult. Coaxial electrospinning is an effective way to realize the combination, which is very strict for the solutions and the synthesis conditions. In this paper, composite pH-sensitive sensors were developed by coaxial electrospinning of polyaniline (PANI) and polyurethane (PU) into core-shell fibers. PU improved the mechanical properties of the sensors. The mechanical properties and conductivity of the sensor can be changed through adjusting the proportion of PANI and PU. By chronopotentiometry in buffer solutions, the sensor worked linearly in the pH range of 2-7 with the sensitivity of - 60 mV/pH and pH change below 0.2 can be detected. It was also proved that the sensor can resist the influence from the changes in temperature, detection time and deformation of the sensor, ensuring the stability in pH detection. Further, by attaching to skin, our sensor showed the response to the pH of small amount of sweat on the skin surface, which suggested the possibility in wearable devices. Graphic abstract