The elastic constantsC11,C33,C44,C13of oriented poly propylene films are measured with Brillouin scattering and are compared with the elastic constants obtained from extruded poly propylene rods. The photoelastic constantsp12,p13, andp31of the extruded rod samples are measured by comparison to a poly(methylmethacrylate) reference scatterer. In the film samples, the relative values of the photoelastic constantsp11,p33,p13, andp31are measured by comparison of the quasilongitudinal and quasitransverse intensities at several directions of sound propagation. Within the experimental error,p13,p31, andp12are found to be unaffected by extrusion or stretching.p11andp33are found to change in relation top31in the film samples. The results are interpreted by considering the chain morphology and the theory of photoelastic interaction. The changes in the Brillouin intensities are due to changes in the elastic constants, rather than the photoelastic constants.