Zinc oxide cluster cations have been analyzed by ion mobility spectrometry using a home-made drift cell combined with a time-of-flight reflectron mass spectrometer. Structural changes from cyclic to tube like structures were observed around n = 8, corresponding to predictions by theoretical calculations. The structures were assigned by comparing with the arrival time simulation using MOBCAL software. We have also observed ion-injection energy dependence of the structures of (ZnO)n(+). The smallest tube structure of (ZnO)6(+) has predominantly been observed at an injection energy of 200 eV. The extraordinary stability of the compact structure at this size has been observed for the first time.