Bicrystalline ZnO nanocombs have been prepared by zinc powder evaporation at 650 degrees C. Structural analysis showed that as-synthesized samples are composed of two crystals that form a twin structure parallel to the (113) plane with the growth direction of the branching nanowires and the main stem closely parallel to (0001) and (0110), respectively. Due to the unique twin structures, both sides of the main stems could be Zn-terminated ZnO(0001) polar surfaces. The chemically active surfaces make the aligned branching nanowires grow from both sides of the main stems, which is consistent with the structure of the obtained bicrystalline nanomaterials. The growth of bicrystalline ZnO nanocombs can be explained by polar-surface dominated growth and twins induced growth mechanisms.