The presented investigations concern the distribution and characterization of keratin waste, derived from the processes of cattle skins, and its use as a filler for carboxylated acrylonitrile-butadiene rubber XNBR. The recovered keratin improves mechanical proprieties such as tensile strength, hardness, resistance to fuel and oil. The addition of keratin in a quantity of five parts per hundred rubber (XNBR) increases the crosslinking density of composites, as testified by the formed ion nodes and the existing mono and disulphide bonds. Electric conductance and water absorption increased with time for elastomers filled with protein. Therefore these composites are biodegradable after their period of use. As a result hydrophilic-hydrophobic protein-elastomeric composites will have usable properties.