A rheo-optical system was used to analyse the nature of the structural changes, other than the well known chain orientation, which can appear during uniaxial drawing of bulk isotactic polypropylene samples with a spherullitic structure. The stretching was performed at room temperature and Raman spectra were simultaneously collected along with stress and strain data to gain insight into the molecular basis of the properties involved in the mechanical process. Some degree of backbone chain deformation is suggested based on observations of the wavenumber shift of some Raman bands, especially those with high contributions of skeletal vibrations. The dependence of the band shift on the applied stress was not linear and this is interpreted in terms of the different average orientation that the polymer shows during the stretching. The band shift and its associated phenomena were reversible as the load was removed.