We have performed the polarization-modulation near-field scanning optical microscopy (PM-NSOM) and photoluminescence NSOM (PL-NSOM) measurements on the InGaN alloy epitaxial layer. Spatial variations in the crystalline quality of nanoscale domains in InGaN film were found by PM-NSOM. It was found that the luminescent property of InGaN correlates closely with the local crystalline quality. Regions with better crystallinity have higher luminescence intensity and longer emission wavelength, while regions with poorer crystallinity exhibit a luminescence of lower intensity and shorter emission wavelength. We show that the combination of PM-NSOM and PL-NSOM is a useful diagnostic tool to the correlation between crystalline and optical properties of the nanostructures. (c) 2007 The Electrochemical Society.