Polypropylene/stearic acid fibers were produced in laboratory conditions from hot homogenous blends. After formation, as-spun fibers were treated in potassium hydroxide and rinsed in water. Supermolecular structure and morphology of fibers were investigated by wide-angle X-ray scattering, FTIR, and scanning electron microscopic (SEM) methods. It was stated that by fibers' formation, thermally induced phase separation takes place. Polypropylene starts to crystallize, while liquid stearic acid is expelled out and forms drops wrapped in polymer matrix. As a result of the crystallization inside fibers the structure with high content of mesophase is formed. During crystallization, interactions between stearic acid and polypropylene are observed. As a result of alkali treatment and rinsing, drops of stearic acid are partially removed. After removal of the stearic acid from the fibers, the porous structure is formed. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012