Abstract: The results of Raman scattering of zinc-blende Zn1-x-yMgyBexSe mixed crystals are reported. From analyzing the polarized Raman spectra, longitudinal and transverse phonon modes corresponding to ZnSe-like, MgSe-like and BeSe-like optical phonon modes are identified. The observed optical phonon modes of the mixed crystals in the BeSe-like spectral region provides experimental evidence that the 1-bond -> 2-mode percolation scheme may apply to the investigated quaternary mixed crystals. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim