The structural, mechanical and electronic properties of the ternary inter-alkali metal oxides KNaO and RbNaO compounds are investigated by using first principle calculations. The structural parameters and atomic positions are in agreement with the experimental values. The bulk, shear and Young moduli, Poisson's ratio, Lame coefficients and Debye temperature have been calculated. The elastic parameters indicate that these compounds have ductile behavior. The calculated band structures indicate that KNaO and RbNaO have an indirect energy band gap. The charge density distributions reveal an anionic character. This theoretical study is likely to stimulate future experimental researches. (C) 2018 Elsevier B.V. All rights reserved.