We have developed a vapor–liquid–phase combined, layer-by-layer epitaxial growth strategy for fabricating ultralong ZnO one-dimensional vertical arrays. A key point is the activation of the second top epitaxial growth by treating shorter arrays in a growth solution. By alternating solution- and VS-growth steps for three times, we can tune the length of the 1D arrays from 41 to 150μm. The arrays were found to show an excellent photoelectrocatalytic activity under UV irradiation, higher than that of high-performance TiO 2 nanotube arrays.