Two types of micro mobile machines, of unimorph and stacked type piezoelectric element, respectively, have been investigated with respect to their basic performance and their mechanism. The geometrical size of both machines is less than 10 nm /spl times/ 10 mm, and their maximum speed on the horizontal plane and their climbable slope were found to be 100 mm/s and 15 degrees, respectively. Concerning the stacked type machine, various experiments have been conducted, and their results have been analyzed to understand the motion characteristics by solving boundary conditions of the elastic vibration equation. The vibration of the machine frames was observed by microscope to supplement the analytical data.