This research explores the longitudinal and latitudinal mechanical properties of injection-molded isotactic polypropylene (iPP) prepared in a uniaxial oscillating stress field by oscillating packing injection molding (OPIM). The methods, processing conditions, and mechanical test results for iPP by conventional injection molding (CIM) and OPIM are described. The mechanical properties in the flow direction (MD) and transverse direction (TD) of the OPIM moldings indicate three types of self-reinforced iPP moldings. The pronounced biaxially self-reinforced iPP specimens exhibit a 55-70% increase of the tensile strength and more than a fourfold increase of the impact strength in the MD, together with more than a 40% increase of the tensile strength and a 30-40% increase of the impact strength in the TD. The OPIM moldings show different stress-strain behavior in the MD and TD.