The appearance of the gamma phase of a polypropylene-containing terpolymer prepared with a Ziegler-Natta catalyst was analyzed, and a novel strategy to make a polypropylene terpolymer which contains a high content of the gamma phase was experimentally sought. Wide-angle X-ray scattering and differential scanning calorimetry measurements have been conducted to investigate gamma-phase formation. Using a mixed flow of both elongational and shear components (a foaming process), we could introduce a lot of nuclei in the melt by flow-induced crystallization (FIC). The large number of nuclei accounting for the structural disorder during crystallite formation was ascribed to be the reason for gamma-phase formation in the terpolymer crystallization. A uniform distribution of defects in the melt crystallization was the key to obtaining a high content of the gamma phase.