A simple and cheap method has been applied to synthesize single-crystal uniform ZnO tubes with high yield in a hydrothermal process using Zn(NO3)2⋅6H2O and methenamine as reaction precursors at low temperature. The products are characterized by XRD, SEM, TEM and SAED. ZnO tubes are uniform single-crystal structures and grow along the  direction. They have straight and regular hexagonal configuration with faceted ends and slippery side surfaces. The growth mechanism of ZnO tubes is investigated and the processing conditions are critical for the formation of ZnO tubes.