In this study, we prepared various superhydrophobic surfaces using ZnO nanorod arrays (ZnO-NR) of different diameters. The contact angle was equivalent to the calculated value if it is assuming that the topmost surface of the rods is a solid-liquid contact area. Oil the superhydrophobic ZnO-NR surfaces, the 5 mu L water droplets slid down by constant acceleration motion. Sliding acceleration was governed by the solid area fraction. The resistance force of the actual measurement was consistent with that calculated using the model.