Single molecule measurements have allowed series of kinetic events of biomolecules to be monitored without interruption. The stepwise movement of molecular motors was measured and analyzed in relation to the hydrolysis reaction of ATP. In the case of kinesin, forward and backward steps occurred stochastically at the same chemical state. The directional movement was explained by the asymmetric potential created by the interaction between kinesin and microtubules. Similarly thermal Brownian movement of myosin during the hydrolysis of single ATP molecules was biased through an asymmetric potential, resulting in directional movement. Thus, single molecule measurements have provided new approaches to analyze the function of molecular motors which often consist of several different events.