Novel polyurethanes bearing carbosilane segments (1a–c) were synthesized. Their thermal and mechanical properties were compared with corresponding reference polyurethanes bearing carbon-based backbone (2a–c). The thermal properties of these polyurethanes were investigated by DSC and TGA. Glass transition temperature was significantly reduced by substituting carbon atom with silicon (1a–c). Moreover, the thermal decomposition temperature of 1a–c was found to be comparable to 2a–c. Furthermore, Young's moduli of 1a–c were lower than those of 2a–c. A large potential of carbosilane unit as a soft segment for building new polyurethanes have been demonstrated in this paper.