Abstract: A process for the preparation of collagen fibers, especially suited for medicinal use, comprising subjecting animal skin, hide or tendons to digestion with a strong alkali until the material has an amide nitrogen content of approximately 0.20 to 0.40 mole per gram, swelling the mass by thorough intermixing with acid, mechanically separating collagen fibers from the mass, de-swelling the collagen fibers with salts or organic solvents, and dehydrating the collagen fibers to approximately 20 to 40 weight % moisture based on the dry weight of the fibers. A plasticizer may be applied to the fibrous mass before dehydration.