Surface morphology of melt-spun polypropylene (PP) filaments, spun from an additive-free PP powder and from a commercial-grade PP with different draw ratios, were examined with atomic force microscopy (AFM). The surface morphology of as-spun filaments was spherulitic. The gradual transformation of the surface structure from a spherulitic morphology to a fibrillar morphology during stretching was studied. In the filaments spun from the commercial-grade PP, the transformation was initiated by deformation of spherulites with a draw ratio of 1.2 and continued with association of lamellar stacks into fibrillar chains with a draw ratio between 1.2 and 2.0. A hierarchical morphological microstructure of fibrils, microfibrils, and nanofibrils was developed with a draw ratio of 4.0. In the filaments spun from the additive-free PP, the association of lamellar stacks into fibrillar morphology occurred considerably later, between draw ratios of 2.0 and 4.0. An oriented lamellar structure was found in these filaments, still with a draw ratio of 4.0.