Isotactic polypropylene (iPP) is used in a wide variety of products, including the rapidly growing area of nonwoven fabrics. A new method based on Raman microspectroscopy is developed to determine the morphology of iPP fibers in complex structures through correlations with specific features of the Raman spectra and the birefringence and Lorentz density of a series of fibers. A good correlation is found between the fourth Legendre polynomial (P-4) of the principle axis of the Raman tensor of the 841 cm(-1) band and the birefringence. Only vibrations that include the C-C-C backbone stretch correlate well with the birefringence. There is a second, empirical correlation between the birefringence and the depolarization ratios of the 841 and 809 cm(-1) Raman bands when the fiber axis is oriented parallel to the laser polarization. The experimental protocol for this empirical correlation is much simpler than for the P-4 correlation while simultaneously yielding improved accuracy. There is another empirical correlation between the Lorentz density and the depolarization ratios of the 841 and 1330 cm(-1) Raman bands. Thus, the birefringence and Lorentz density of iPP fibers could be determined quantitatively using polarized Raman microspectroscopy.