The low-frequency Raman spectra of alkali halide AX (A = Na, K, Rb; X = Cl, Br) aqueous solutions with various temperatures and concentrations are investigated. We have found that at the supercooled temperature region the relaxation time of the KX and RbX aqueous solutions becomes shorter than that of pure water. Since in these solutions the viscosity decreases with increasing concentration, this result suggests that the relaxation time of the electrolytic solutions in the Raman region is strongly correlated with the viscosity. Moreover, through comparing the spectral profiles of the relaxation mode among AX aqueous solutions we demonstrate that the pattern of the concentration dependence of the relaxation mode parameters such as the activation energy changes between NaX and (KX,RbX) aqueous solutions.