Microporous polypropylene fibers were prepared by stretching polypropylene fibers containing CaCO3 filler. The properties of the resultant fibers are controllable by adjusting the filler content and the stretching ratio. Also, it is elucidated that the fibers have a fine texture of polypropylene fibrils, in which the filler particles are dispersed. Furthermore, the CaCO3 filler was removed by treating the fibers with an HCl-CH3OH solution, and their properties were also investigated.