Structural evolution of gel-spun ultra-high molecular weight polyethylene fibers with high concentration solution via hot stretching process was investigated by in situ small-angle X-ray scattering, in situ wide-angle X-ray diffraction measurements, scanning electron microscopy, and differential scanning calorimetry. With the increase of stretching strain, the long period continuously increases at relative lower stretching temperature, while it first increases and then decreases rapidly at relative higher stretching temperature. The kebab thickness almost keeps constant during the whole hot-stretching process and the kebab diameter continually decreases for all stretching temperatures. Moreover, the length of shish decreases slightly and the shish quantity increases although there is almost no change in the diameter of shish crystals during the hot stretching process. The degree of crystal orientation at different temperatures is as high as above 0.9 during the whole stretching process. These results indicate that the shish-kebab crystals in ultra-high molecular weight polyethylene fibers can transform continuously into the micro-fibril structure composed mostly of shish crystals through the hot stretching process. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 225-238