Solid solutions of NaCl, KBr and KI were prepared by the melt method for the first time. Densities and refractive indices of all the prepared solid solutions were determined and also used for the estimation of the bulk composition in the crystal. Lattice parameters and thermal parameters like Debye-Waller factor, mean square amplitude of vibration, Debye temperature and Debye frequency were determined from the X-ray powder diffraction data. The observed lattice parameters showed the existence of three phases in solid solutions each nearly corresponds to NaCl, KBr and KI. The thermal parameters show a highly non-linear bulk composition dependence.