The room temperature Raman spectra of the Ga 0.5 Al 0.5 As and the In 0.52 Al 0.48 As epilayer grown on [ n 11] oriented substrates were measured in various back scatterng geometries. The relative intensity of TO modes and LO modes in those samples shows a regular variation with differently oriented substrates in the experiments. By comparing experimental data with Raman scattering selection rules for the zincblende structure epilayer grown on [ n 11] oriented substrates, it was found that the present calculations are in good agreement with the experimental results.