Filling free volume pores of the amorphous phase with the molecules of low molecular weight modifier leads to a complete elimination of the cavitation during tensile drawing. Such way of modification of a solidified material makes the polypropylene/modifier system a model system that enables the analysis of the influence of cavitation on thermomechanical properties and the mechanisms activated during its deformation. In this paper we have presented the influence of cavitation on the intensity of the lamellae fragmentation. In the case of cavitating material, on the basis of X-ray measurements and scanning electron microscopy, we have observed substantial decrease of the undisturbed crystallites lengths during its deformation up to 50-55% of their initial value. The deformation of noncavitating material proceeded with smaller decrease of average crystallites lengths by only 15-20% of their initial value. The changes of the SAXS's long period of noncavitating polypropylene indicated that only a small fraction of lamellae stacks that are oriented parallel to the tensile direction undergo fragmentation. This type of fragmentation is connected with excessive lamellae thinning and interfacial instabilities but by no means by cavitation.