The effect of radiation of a gray gas in a square cavity with double diffusive natural convection is presented. The regime flow studied range from a thermal Rayleigh number of 104 to 1011 and buoyancy ratio from 0.5 to 2.0. The governing equations of fluid-flow, heat transfer and radiative transfer equation are solved by the finite volume method. The results show the effect of radiatively participating media plays an important role in the heat and mass transfer study doing oblique stratification. The velocity and turbulent viscosity increases about 80% and 22%, respectively, and decreases the convective Nusselt number 13%. The increase of buoyancy ratio increases the mass transfer until 26%. Finally, a practical correlation for computing the convective and radiative Nusselt numbers as well as the Sherwood number is proposed.