The nonlinear relaxation behavior of olefin multiblock copolymers subjected to step shear strains has been investigated. Compared to homogeneous polymer, a two-step relaxation behavior was identified in olefin multiblock copolymers, with the faster one for the chain relaxation and the slower one for the domain relaxation. It is found that the domain relaxation has stronger strain dependence than the chain relaxation. Large repeated step strains can cause longer relaxation process of domains as compared to the single step strain test. The prolonged domain relaxation and nearly constant relaxation plateau modulus are ascribed to the coarsening of domain as well as the increase of the volume fraction of domains, which indicates the accelerated mesophase separation of olefin multiblock copolymer under large strains. (C) 2017 Elsevier Ltd. All rights reserved.