We report a concept of using Rayleigh backscattering signature based unclonable optical fiber identification (OFID) for security-based applications. Due to the inherent manufacturing features of optical fibers, the random Rayleigh backscattering pattern within an optical fiber can be used for identification. We also experimentally demonstrated the OFID idea. Cross correlation in the spatial domain and encoding techniques are applied to verify the authenticity of OFID. Also, it has been demonstrated that the proposed OFID device can survive the high-temperature harsh environment. This robust, reliable, and flexible OFID method has great potential for a variety of applications, such as security, recognition, encryption, identification, and authentication. .