This letter reports a simple and versatile approach for extracting bionanofibers from natural materials using the ultrasonic technique. Bionanofibers have been fabricated from various materials, e.g., spider and silkworm silks, chitin fibers, collagen, cotton, bamboo, and ramee and hemp fibers. The obtained nanofibers have uniform diameters in the range of 25-120 nm and possess the optimized hierarchical structures and superior properties of natural materials which have formed after the evolution of many millions of years. This methodology might be valuable to provide a convenient, versatile, and environmentally benign fabrication method for producing bionanofibers at an industrial scale.