Thermoplastic polyurethane elastomers（TPUs）can be given as one of the most popular polar thermoplastic elastomers（TPEs）. The TPUs are usually composed of soft segment formed with polymer glycol and hard segment done with diisocyanate and chain extender. Though olefinic TPEs are simple chemical and micro-phase structures, TPUs are very numerous chemical and micro-phase structures. Physical properties of the TPUs are strongly dependent on micro-phase structures. In this review, it was described on the origin of rubber elasticity of polyurethane elastomers, the direct observation of the microphase separated structure of the TPUs using AFM, and the molecular design factors for high performance TPUs.