This paper reports an analytical and numerical study of double-diffusive natural convection in a non-Newtonian power-law fluid contained in a horizontal rectangular enclosure submitted to uniform heat and mass fluxes along its short vertical sides, while the horizontal ones are insulated and impermeable. The first part from this study is devoted to the numerical solution of the governing equations, and the effect of the governing parameters, namely, the cavity aspect ratio, A, the Lewis number, Le, the buoyancy ratio, N, the power-law behavior index, n, and the generalized Prandti, Pr, thermal Rayleigh, Ra-T, numbers, is examined. In the second part, an analytical solution, based on the parallel flow approximation in the case of a shallow cavity (A >> 1), is proposed and a good agreement is found between the two types of solutions. (c) 2008 Elsevier Ltd. All rights reserved.