Bicrystalline ZnO nanocombs have been prepared by zinc powder evaporation proces s at 650℃. The structure of bicrystalline ZnO nanocombs was characterized by XR D, HTEM, SAD, etc., which indicate that the as-synthesized sample are composed of two crystals that form a twin structure parallel to the (1 1 3) plane with th e growth direction of the branching nanowires and the main stems closely paralle l to〈0 0 0 1〉 and〈0 1 1 0〉，respectively. Due to the unique twin structures, both sides of the main stems could be Zn-terminated ZnO (0 0 0 1) polar surface s, which are chemically active. Therefore the aligned branching nanowires can be grown from both sides of the main stems, which is consistent with the structure of the bicrystalline nanomaterials we have obtained. The growth of bicrystallin e ZnO nanocombs bears direct evidence to the polar-surface dominated growth mech anism of the ZnO nanomaterials.