A wireless resonant micro-actuator for untethered micro-robots. The wireless resonant micro-actuator includes at least two magnetic bodies that are resiliently connected to one another by a resilient member to form a spring-mass system. A magnetic field generator generates a pulsating or oscillating external magnetic field that creates a magnetic force between the at least two magnetic bodies. The at least two magnetic bodies are capable of being mechanically oscillated to resonance with respect to one another. A converter converts the oscillatory motion of the at least two magnetic bodies to create useful motion.