Energy harvesting performance of an efficient flexible bio-piezoelectric nanogenerator (BPNG) is demonstrated, where “bio-waste” transparent fish scale (FSC), composed of self-assembled and ordered collagen nano-fibrils, serves as a self-poled piezoelectric active component, exhibiting intrinsic piezoelectric strength of −−5.0 pC/N. The dipolar orientation (∼19%) of the self-polarized FSC collagen is confirmed by the angular dependent near edge X-ray absorption fine structure spectroscopy.