In this article, the effect of double diffusion in a saturated porous ferrofluid layer salted from below under the influence of an internal heat source has been studied. The Darcy model is employed for the momentum equation and a two-phase model is used for the energy equation. For the linear anal-ysis, the normal mode technique is applied and the numerical calculations are carried out using the Chebyshev pseudospectral method. The nonlinear analysis is made with the minimal representation of the truncated Fourier series. The behavior of internal heat parameter (ξ), interphase heat transfer (H1), porosity modified conductivity ratio (β), solutal Rayleigh number (Rs), Lewis number (Le), and Langevin parameter (αL) on the stability of the system is discussed. Streamlines, isotherms, and isohalines are plotted for steady nonlinear cases. Nusselt number Nu and Sherwood number Sh represent the heat and mass transfer across the porous layer respectively and these are calculated by solving the finite-amplitude equations using a Runge–Kutta–Gill method. © 2022 by Begell House, Inc.