Nanocomposite fibers of ultra high molecular weight polyethylene (UHMWPE) and organic montmorillonite (OMMT) were successfully prepared by a melt-spinning process. The evolution of the microstructures of the nanocomposite fibers in the drawing process was preliminarily studied by X-ray diffraction (XRD), differential scanning calorimetry, and small-angle X-ray scatters. With the increase of draw ratio values, the crystallinity of the nanocomposite fibers increased, the grain size decreased, and the folded chain crystals gradually transformed into extended chain crystals. The results suggested the evolution of the nanocomposite fibers was similar with that of the fibers made by gel-spun drawing process. The addition of OMMT in UHMWPE improved the fluidity of the composites yet without affecting the crystal structure of UHMWPE in the drawing process. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3930-3936, 2013