Structural development of ultra-high strength polyethylene fibers via hot-drawing processes of as-spun gel fibers was investigated by means of transmission electron microscopy. It is found that the shish-kebabs developed in both the as-spun and drawn fibers can be transformed continuously into the micro-fibril structure composed mostly of the shish structure through the hot-drawing process. The structure transformation involves a drastic decrease in diameter of the kebab plus the shish but almost no change in the shish diameter. This result suggests that the chains in the kebabs are incorporated into the shishs and consumed to extend the longitudinal dimension of the shishs during the drawing process. The proposed new deformation model well explains the relationship between the fiber morphology and their mechanical properties: the tensile strength and modulus of the fibers can be determined by the number of the shish in the fiber and the macroscopic diameter of the fiber, which are apriori determined at the spinning process. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1861-1872, 2010