AbstractIn recent years, the strain sensors, which can be fixed on human skin to monitor movement, have attracted a considerable attention. In this study, the walnut shell powder was carbonized and mixed with polydimethylsiloxane, followed by encapsulation to prepare a highly flexible strain sensor. The obtained sensor was tested for the electrical and sensing properties. The experimental results revealed that the sensor is stable and reliable in the range of 0% to 40% strain response, while the effective working frequency of the sensor is in the range of 0.01 to 0.5 Hz. Moreover, the carbonized the walnut shell powder/PDMS prepolymer and its curing agent (PDMSCA) strain sensor exhibited an excellent fatigue resistance. No significant attenuation phenomenon was observed after 1000 cycles of stretching. The strain sensor was then attached to a volunteer throat, knee, elbow, and fingers joints. The corresponding human movements determined obvious sensing response and repeatability. This work proposes a new flexible strain sensor based on environmentally friendly materials, which is obtained by means of a facile preparation method. Hence, this work can open up new avenues for the development of novel and effective strain sensors using cost‐effective carbonized materials as filling materials.