Using near-field optical microscopy we present experimental results on spatially resolved PL spectra of GaAs quantum wire (QWR) structures with a lateral width of 15 nm fabricated by selective growth method. The geometries of the samples make it possible to observe the luminescence from a single QWR structure. The typical fluctuations of the PL peak energy from different QWRs is estimated to be about 5 meV. To reduce the diffusion of carriers from barrier regions, PL spectra are observed by selective excitation of the QWR. A PL line width of 5 meV, which is about ten times narrower than that of the conventional PL measurement, is observed.