The high-pressure behavior of zinc oxide (ZnO) nanotube has been investigated to 38.7 GPa by in situ synchrotron x-ray diffraction in a diamond anvil cell at room temperature. The transformation from the hexagonal wurtzite (B4) to the cubic rocksalt (B1) phase started at 10.5 GPa and completed at 18.4 GPa. The initial transition pressure of nanotube is found identical to that in bulk crystal but lower than in nanodots, while the completion pressure of nanotube is identical to that in nanodots but higher than in bulk crystal. This indicates that the c -direction of hexagonal ZnO crystal plays a more important role in the initiation of the phase transition, and the a -direction controls its completion. These prove that the B4-B1 transition undergoes a hexagonal path. It is also found that the c/a ratio of the B4 phase decreases slightly before the phase transition and tends to increase during the phase transition, which is also consistent with the theoretical hexagonal-path model. The bulk moduli of B4 and B1 phases were, respectively, 152 and 242 GPa, indicating higher energy is required to compress ZnO nanotube than ZnO bulk crystal only in the B1 phase.