The results of the investigations of photoluminescence and photoluminescence excitation spectra together with the transmission electron microscopy structural analysis of Al_xGa_1-xAs nanowires grown by molecular beam epitaxy with nominal aluminum content of 0.2 - 0.7 are presented. It is shown that the investigated nanowire possess wurtzite phase and the spectral positions of their luminescence band differ significantly from the bulk sphalerite type alloys of similar content.