This paper investigates the effect of mesophase separation on the crystallization behavior of olefin block copolymers (OBCs) with different octene contents, which were synthesized by chain shuttling technology Crystallization always occurs simultaneously but competitively with mesophase separation in OBCs Because of the reason that the crystallization temperature is lower than the mesophase separation temperature for the OBCs, the mesophase separation can start first, large portions of the crystallizable hard blocks are confined in the mesophase-separated domains and could not contribute to the formation of radial lamellar stacks In addition, the mesophase separation creates a stereo-hindrance effect, crystal lamellae could only grow through the interstitial space between the dispersed domains As a result, large and compact crystals could not be formed As the octene content increased in the sample mesophase separation becomes more and more dominant, and the crystal morphology degrades sharply from spherulites to fragmentary lamella structures It is found that increasing the annealing time during development of the mesophase separated structure has a similar effect to increasing the octene content in the sample However, all of the OBCs can form nearly the same crystalline morphology if the mesophase separation is suppressed, from which we can postulate that the nature of crystallization due to the crystallizable hard blocks in OBCs should be similar