Structure changes around the crack tip of natural rubber vulcanizates filled with carbon-black were investigated after a cycle of stretch-retraction. On the extension line of the crack, formation of a valley-like dent was newly found.The depth of the dent was about 10 μm. By the diffraction mapping using the micro X-ray beam, localization of crystals of paraffin, which has been mixed as plasticizer, along the valley-like dent was disclosed. These findings indicate the occurrence of large-scale mass transfer which leads to three-dimensional transformation and segregation of the low molecular weight material along with the strain-induced crystallization around the crack tip.