The mesophase separation and crystallization as well as the elastomeric properties of olefin multi-block copolymers (OBCs) are studied. The solid state morphologies of the OBCs are determined by the competition between mesophase separation and crystallization of hard blocks. The OBC with lower Delta(C8) (octene content difference between soft and hard blocks) displays a spherulitic superstructure, while the OBC with higher Delta(C8) exhibits mesophase separation. The two OBCs show very different elastomeric properties. Wide-angle X-ray scattering shows that the two OBCs have different deformation mechanisms. It is proposed that the cooperative deformation of crystalline phase makes an important contribution to the elastomeric properties. (C) 2011 Elsevier Ltd. All rights reserved.