The Raman spectra of neodymium(III), gadolinium(III) and thulium(III) perchlorate solutions of varying salt molalities were measured in N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) and their mixtures by titration Raman spectroscopy at 298 K. The in-plane OC–N bending vibration at 660 cm−1 of DMF and the stretching N–CH3 vibration at 740 cm−1 of DMA show an appreciable shift to a higher frequency upon coordination of the solvent molecules to the metal ion. In DMF–DMA mixtures, the magnitude of the shift for the δ(OC–N) and ν(N–CH3) vibrations of bound solvent molecules, ΔνDMF, and ΔνDMA, respectively, depends on the solvent composition, and the variation profile of ΔνDMA is in parallel with that of the Ln–O(solvent) bond length. The number of solvent molecules bound to the metal ion or the individual solvation number in a solvent mixture, nDMF and nDMA for DMF and DMA, respectively, were evaluated by analyzing the intensity decrease of the free solvent bands with increasing molality of the metal ion. It is indicated that a strong solvation steric effect operates among bound solvent molecules, i.e., the total solvation number decreases with increasing DMA content, and the variation profile depends on the metal ion. The individual solvation number of DMA was found to be 3 at around xDMA = 0.4 for all the metal systems examined.