A study utilizing isotactic poly(4-methyl-1-pentene) (PMP) was undertaken to investigate a three-stage process (melt-extrusion/annealing/uniaxial-stretching) (MEAUS) employed to produce microporous films. The results of this study will be reported in the course of two articles. In this first part, three PMP resins were melt-extruded into tubular films (blowup ratio; BUR = 1), where the resins each differ in weight-average molecular weight (M-w). Specific attention was focused upon the morphological and crystal orientation results as a function of the melt-relaxation times as influenced by the resin characteristics and the processing parameters. The results of a number of melt-extrusion conditions are presented. A stacked lamellar morphology was obtained in each case; however, the type of stacked lamellar morphology, planar or twisted, and the orientation state was found to depend upon both the resin characteristics, specifically M-w, and the melt-extrusion conditions. Atomic force microscopy and wide-angle X-ray scattering (WAXS) were the main techniques utilized to study the melt-extruded films, while oscillatory shear measurements, in conjunction with a Carreau-Yasuda analysis, aided in differentiating the melt-flow behavior of the three resins.