Electricity harvest from ubiquitous water has been endeavored, using nanogenerators based on carbon nanomaterials, to acquire renewable and clean energy and cope with fossil depletion and pollution as well. Meanwhile, though many biological organisms can harness water for bioelectricity, it is still challenging to produce biological nanogenerators based on biological nanomaterials with billions of tons of annual production in nature. Herein biological nanofibrils, including cellulose, chitin, silk fibroin, and amyloid, are produced either by liquid‐exfoliation of biomasses or by supramolecular assembly of bio‐macromolecules. With the intrinsic hydrophilicity and charged states, they can capture moisture from air and form hydrated nanochannels, in analogue to ionic channels of cytomembranes. When exposing their aerogels to moist air flow, there is a balance of water absorption and evaporation, thus producing a streaming potential and an open‐circuit voltage across the aerogel. With flexibility, sustainability, biocompatibility, and biodegradability, these biological nanogenerators can harvest electricity from moist air flow in nature (e.g., wind, respiration and perspiration) and in industry, and serve for environmentally‐friendly, low‐cost, high‐efficiency, wearable, and miniaturized power devices. Biological nanofibrils, having intrinsic hydrophilicity and diverse charged states, can capture moisture and form hydrated channels like the ionic channels of cytomembranes. Their aerogels are able to produce a streaming potential when exposed to moist airflow. These biological nanogenerators could harvest energy from nature and industry (e.g., moist wind, respiration and perspiration), and serve as sustainable, high‐efficiency and wearable power devices.