Formation mechanism of a remarkable type of pseudoperiodical multi-twinning nanostructures has been investigated by using ZnSe nanowires as a model system. Transmission electron microscopy observations indicate that the nanowires are guided by a catalyst particle, and alternating twins with {1 1 1} twin boundary are extended. The crystalline orientations of the catalyst particle prefer to take the same as that of nanowire. The misfit dislocations in the interface are observed for the first time. They are used to release the large mismatch between catalyst and nanowire. The remaining mismatch energy is released by forming twin boundary. The strain energy is cumulated and released periodically, so the pseudoperiodical multi-twinning nanostructures are formed. (C) 2007 Elsevier B.V. All rights reserved.