Two kinds of ZnO twinning nanostructures, three-edged nanobelts and hexagonal-disk strings, were successfully fabricated through a thermal evaporation method. The detailed microstructure and composition of the nanostructures were characterized by transmission electron microscopy. In spite of their differences in morphology, they have the same (0 113) and (01 11) twin boundaries. A {0 113} twin core is introduced to explain the formation of the twin boundaries. The differences in morphology may be caused by the changes of surface energy and supersaturation level induced by group III element doping.