Spinels are very important minerals in terrestrial and extraterrestrial rocks as well as materials of high relevance from a gemological and technological point of view for their remarkable physical properties. Ten synthetic spinels belonging to the MgAl2O4– CoAl2O4 and to the MgAl2O4–MgCr2O4 solid solutions have been studied by Raman spectroscopy to examine how substitution of the divalent and trivalent cation affects the Raman modes. Raman investigation on the Raman spectral change into a solid solution can be used to obtain semi-quantitative chemical information. The spinels were synthetized by flux growth method and analyzed chemically by electron microprobe and structurally by single-crystal X-ray diffraction. Raman spectra were collected with a Jobin Yvon LabRam micro-spectrometer using two different laser wavelengths. A 632.8 nm He-Ne laser was used for the samples with high Cr content to avoid the fluorescence, while in the samples containing Co the spectra were recorded with a 473.1 nm wavelength from a solid state laser. When the substitution Co2+→Mg occurs in the MgAl2O4 – CoAl2O4 series, a continuous and monotonic shift of the five Raman modes is observed for all Raman modes. The Eg, F2g(2) and F2g(3) modes show a shift toward lower wavenumbers with the increase of the cobalt content, in agreement with the change in the divalent cation mass. The F2g(1) and A1g modes exhibit a slight shift toward higher wavenumbers along the series revealing a dependence of these modes on the trivalent cation. In the CoAl2O4 end-member the most characteristic peak at 516 cm-1 is attributable to the F2g(2) mode. This peak can be followed along the series and a good linear correlation between the wavenumber of the F2g(2) mode and the Co content (Cotot) is obtained. In the MgAl2O4 – MgCr2O4 series, all observed Raman modes exhibit one-mode behavior, with the exception of the Eg mode. The Eg mode of the Cr-poor spinels at ~405 cm-1 decreases its intensity with the increase up to ~50-60% of the chromite content. From this composition another Eg mode starts to growth at ~450 cm-1 becoming well defined in the pure chromite end-member. The F2g(3) and A1g modes show large shifts demonstrating a strong influence of the trivalent cation. In addition, a linear correlation can be observed relating the variation of the A1g mode and the local Cr-O bond distances along the series.