An exemplary lens actuator includes a movable unit, and a fixed unit. The movable unit includes a hollow body, and a plurality of first guiding members formed on the hollow body. The fixed unit includes a hollow cubic main body, and a plate body disposed on the top end of the hollow cubic main body. The hollow cubic main body and the plate body cooperatively define a receiving cavity for receiving the movable unit therein. The plate body faces the movable unit, and includes a through hole defined in the center of the plate body for allowing light to pass therethrough, and a plurality of second guiding members formed on the plate body. The second guiding members are coupled to the respective first guiding members for constraining the movable unit to move along the central axis of the through hole.