A threelegged resonant vibration driven robot using piezoelectric actuator is presented in this paper. The dynamical equations of the horizontal locomotion is established as one of the three legs vibrating in resonant condition. Numerical results illustrates the motion mechanism and the effect of anisotropic friction on direction and velocity of the robot. The approximate relationship between the frequency of piezoelectric actuator and the velocity of locomotion is obtained. The governing equation of inplane vibration for a curved beam is developed to calculate the natural frequencies and the corresponding mode shapes. Based on this equation, three sets of geometrical parameters for the curved legs are devised. It is found that their frequencies are respectively different. The robot prototype is also created according to these parameters. The planar locomotion is accomplished through robot testing by switching the frequencies of alternating voltage applied on piezoelectric actuator to the shift resonant among the legs. Experimental results reasonably match with the numerical simulation.