A new inchworm micromotor using new electrostatic in-plane twisting microactuators has been designed, fabricated and characterized for nano-resolution manipulators. The proposed twisting mechanism was implemented employing a pair of differential electrostatic actuators with a high stiffness in the driving direction for stable positioning. The electromechanically coupled motion of the voltage–displacement relation was analyzed using a finite element method (FEM), confirming that the twisting actuator makes a tiny step movement efficiently. The proposed actuator was fabricated on a silicon-on-insulator (SOI) wafer with the device footprint of 2.2 × 2.8 mm², and its nano-stepping characteristics were measured by an optical interferometer consisting of an integrated micromirror and optical fiber. The fabricated inchworm motor showed a minimum step displacement of 5.2 ± 3.8 nm (2σ) and 4.1 ± 2.9 nm (2σ) for cyclic motion in the +y- and the −y-directions, respectively, with the gripping voltage of 15 V and differential voltage of 1 V. As a result, the proposed inchworm micromotor could operate with a stroke of 3 µm and a bi-directional step displacement of less than 10 nm. The step displacement is the smallest value of in-plane-type micromotors so far, and its magnitude was controllable up to 120 nm/cycle by changing the differential voltage.