We present a micro linear piezoelectric ultrasonic motor, which can be used for zooming and autofocusing features in camera modules inside cellphones and endoscopes, it consists of a cuboid stator with a hole and an elastic cylindrical slider. The motor design, in which the slider inserted into the stator hole expands outward, enables a hollow structure for an optimal preload for enhancing the motor thrust force, (n this study, we model the relationship between the dimensions and the preload to quantify the preload value and clarify the design methodology. The size of the prototype stator with piezoelectric elements measures 2,6 mm in height and width and 2.2 mm in depth (the length in slider travel direction). There is a hole of 1,7 mm in diameter at the stator center, and the slider inserted into the hole operates when voltages are applied to the piezoelectric elements. Applying an optimized preload, we evaluate the fundamental characteristics of the motor in experiments, A thrust force of approximately 40 mN and a resolution of about 1 μm were obtained, which may satisfy the specification of a certain type of camera modules.