Photoluminescence IPL) spectra and scanning near-field optical microscope (SNOM) images have been measured at low temperature to investigate the compositional fluctuations in GaNxAs1-x epilayers grown on GaAs by metalorganic vapor-phase epitaxy. Time-resolved PL has been employed to study the optical transitions and their dynamic processes. Our results suggest that the PL emission from GaNxAs1-x epilayer at low temperature is dominated by localized exciton recombination induced by compositional fluctuations. Furthermore, we directly observed the distribution of the compositional inhomogeneity in the GaNxAs1-x samples even with a small N-content of 0.5% by measuring SNOM images. The emission spot size of less than 1 mum is estimated for the GaNxAs1-x (N = 0.5%)epilayer, and its size tends to decrease with increasing nitrogen concentration.