Abstract: Biased transportation in asymmetric systems widely exist in nature. The macroscale theory indicates that breaking of the spatial inversion symmetry and external fluctuations with a certain auto-correlation time are two requirements for biased transportation. Thus, it is generally believed that thermal noise alone cannot induce biased transportation in molecular-scale asymmetric systems. With the development of experimental technology and simulation methods,biased transportation has been observed in these systems even without external fluctuations. This article describes some recent theoretical research on biased transportation induced by thermal noise in molecular-scale asymmetric systems, and the necessary conditions.