An efficient bio-piezoelectric nanogenerator (BPNG) is fabricated from the fish swim bladder (FSB), composed of well-aligned natural collagen nano–fibrils. The self-alignment of highly ordered structure in the FSB collagen has been confirmed by angular dependent near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Compressive normal stress by human finger can able to drive the BPNG that generates an open-circuit voltage of 10V and short-circuit current of 51nA. The generated electricity from the FSB instantly turns on more than 50 commercial blue light emitting diodes (LEDs), indicates to use as a sustainable power source in portable electronic devices where the bulky battery counterpart can be avoided. The instantaneous piezoelectric power generation (~4.15μW/cm2) and substantial energy conversion efficiency (~0.3%) of BPNG promises an emerging application, particularly to built self-powered biomedical sensors because collagen itself one of the most abundant protein available in human body.