Raman spectra of the mixed crystalline oxides of the (1 - x)TeO₂ + xTeO₃ (x = 0, 1/4, 1/2, 1) series were recorded and simulated by using the DFT calculations. Good agreement between observed and calculated Raman spectra makes it possible to establish unambiguous assignment for all prominent Raman lines. This result gives an insight into relations between structural peculiarities and observed spectral features for the crystals promising as nonlinear optical materials. Highlights • Several mixed TeO₂-TeO₃ crystals were synthesized by solid-state chemistry • DFT calculations well describe structures and phonon spectra of TeO₂-TeO₃ oxides • Raman lines can be assigned to internal vibrations of TeO₄ and TeO₆ polyhedrons • Observed Raman bands can be used as fingerprints of different structural units.