Self-assembled nanowires have attracted much attention due to their potential applications in electronics and optoelectronics. A recent interest in Mn catalyzed GaAs nanowires are due to their potential use in spintronic devices at nanoscale. High densities of Au- and Mncatalyzed self-assembled GaAs nanowires (NWs) with diameter in the range of 20 to 200 nm and length of few microns were synthesized by molecular beam epitaxy (MBE) on different substrates at varied substrate temperatures. These nanowires were investigated by means of μ-Raman spectroscopy at room temperature. The Raman spectra from NWs show an energy downshift and a broadening of the LO and TO phonon lines that differ from those of epitaxial GaAs. We suggest that those downshift and broadening are due to the relaxation of the q=0 selection rule in the presence of structural defects in the nanowires. The results indicate that the use of Mn instead of Au as growth catalyst does not affect the structural quality of the nanowires drastically.