[en] The Raman scattering by phonons and magnons was studied for the first time in the polycrystalline solid solutions Ni_cMg_1-cO. The experimental Raman spectrum for c = 0.9 is similar to that of NiO and consists of six well resolved bands, whose origins are the disorder-induced one-phonon scattering (bands at 400 and 500 cm^-1), two-phonon scattering (bands at 750, 900, and 1100 cm^-1), and two-magnon scattering (the broad band at ∼ 1400 cm^-1). We found that the dependence of the two-magnon band in solid solutions on the composition and temperature is consistent with their magnetic phase diagram. We also observed that the relative contribution of two-phonon scattering decreases strongly upon dilution with magnesium ions and disappears completely at c < 0.5. Such behaviour is explained in terms of a disorder-induced effect, which increases the probability of the one-phonon scattering processes