Double-diffusive natural convection flow in square enclosure filled with nanofluid is studied in this paper. Water based nanofluid containing various nanoparticles including Cu, Ag, $Al2O3$, and $TiO2$ is used in the numerical analysis. The upper and lower walls of the enclosure are well insulated and impermeable and the left and right walls are imposed to constant temperatures and concentration. Laminar regime under steady state condition is considered. The Maxwell–Garnett model is used to predict the ratio of thermal conductivity. The system of conservation equations consisting of continuity, momentum, energy, and solute concentration in dimensionless form are solved by using finite volume SIMPLE algorithm. Results are presented for different values of the governing parameters Rayleigh and Lewis number, in terms of streamlines, isotherms, isoconcentration, local Nusselt number, and local Sherwood number. The effect of nanoparticle volume fractions are also discussed on heat transfer characteristics in the cavity.