High-performance triboelectric nanogenerators (TENGs) are usually made of expensive, unsustainable, and non-biodegradable materials, limiting their development for wearable applications and posing environmental problems for their disposal. Here, we mitigate this challenge by reporting a highly polarizable, low-cost, and biodegradable tribopositive material, made of poly-ε-caprolactone (PCL)/ethyl cellulose (EC) biocomposite. PCL (weakly polarizable, but mechanically robust) and EC (highly polarizable, but mechanically weak) learn from each other’s strengths and complement each other’s weaknesses. The obtained PCL/EC-based TENG reached a peak power density of 157.17 mW/m2 at optimized 6 wt % EC (at 40 MΩ load, 11 N), enhanced by 46 times. Thanks to the good flexibility, high tensile mechanical property, remarkable stability, and biodegradability, TENG can be comfortably attached on the human body as a wearable motion sensor, in addition to energy harvesting applications. Our work greatly contributes to the development of environmental sustainability, which results from reduction of electronic waste generation. Display omitted •An effective tribopositive PCL/EC material is desired•The high-performance PCL/EC biocomposite shows good biodegradation property•Flexible TENG can be conformably attached to the human body as a wearable sensor Fan et al. propose a highly polarizable, low-cost, and biodegradable tribopositive poly-ε-caprolactone/ethyl cellulose material by controlling the mass ratio of ethyl cellulose. In addition to energy harvesting applications, the flexible TENG can also be conformably attached to the human body as a wearable motion sensor.