Due to the special structure of a nanotube (NT), the different potential from piezoelectricity can be naturally divided by the hollow of the tube when the NT is bent or deformed. Furthermore, both the bent/deformed inner and outer wall can form a steady voltage/current, which might enhance the output voltage/current. We demonstrate a direct‐current nanogenerator (NG) based on zinc oxide (ZnO) NT arrays driven by an ultrasonic wave. The average output voltage is ca. 0.10 mV and the current density is ca. 0.069 μA/mm2. Our study shows that the maximum power output of the ZnO NT array NG is 0.112 nW and the power density is 1.4 nW/cm2. The success of energy harvesting from ZnO NTs reveals the potential of using nanogenerators for tubular piezoelectric materials.