The process of cavitation during tensile deformation of polypropylene was studied. It was shown that in injection-molded polypropylene samples cavities appear in the center of a sample shortly before yielding. With increasing deformation the cavities change their size, number, and orientation from elongated perpendicular to parallel to deformation. The cavitation process is visible also as a rapid increase of volume of deformed material. The cavitation could be suppressed by changing internal morphology of polypropylene by fast cooling. The samples prepared by compression molding followed by quenching, with less perfect crystals, were able to deform by plastic deformation of crystals without cavitation. However, for faster draw rate the cavitation in amorphous phase was preferred again due to stronger response of crystals.