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. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)