We fabricated original probes for the near-field scanning optical microscopy (NSOM) with polarization-preserving optical fibers, and succeed polarization observation in guide-collection-mode NSOM. The polarized guide-collection-mode NSOM technique revealed the polarized properties of propagation light within a polymeric optical waveguide by separating independent polarization components. Using the polarized NSOM technique, we characterized the influences of defects and weak stresses within the waveguide. For the characterization, we intentionally printed an indentation in the vicinity of the waveguide, then evaluated the resulting influences from the NSOM images taken around the indentation. When transverse magnetic (TM) polarized light enters a waveguide, the light intensity becomes greater on the near side of the indentation than on the far side, as measured by a linearly polarized component perpendicular to the direction of light propagation. Under the polarization conditions of incident light and collection, it is expected that only the polarization-independent component will be observed and the electric field therefore does not become large. However, if scattering phenomena are present, the electric field should have a non-zero value. The most likely origin of this scattering is microdefects in the polymer generated by the stress-strain field at the interface between the waveguide and the cladding region around the indentation. These microdefects, which are generally a disorder in molecular chains, cause Rayleigh scattering. Finally, it is important to keep in mind that the polarized guide-collection-mode NSOM technique is capable of detecting defects or weak stresses in the nanoscale range within an optical waveguide.