An analytical and numerical study is reported of steady-state natural convection in a two-dimensional rectangular porous cavity saturated by a non-Newtonian fluid. The enclosure is heated and cooled isothermally from the vertical sides, while the horizontal walls are adiabatic. The modified Darcy power-law model proposed by Pascal (1983) is used to characterize the non-Newtonian fluid behavior. In the large Rayleigh number limit, the boundary-layer equations are solved analytically upon introducing a similarity transformation. The core structure is determined using an integral form of the energy equation. Numerical integrations are carried out using the Runge-Kutta method. Solutions for the flow and temperature fields and Nusselt numbers are obtained in terms of a modified Rayleigh number R, the aspect ratio of the cavity A, and the power-law index n. A numerical study of the same phenomenon, obtained by solving the complete system of governing equations, is also conducted, and results are reported in the range 10 2 ≤ R ≤ 10 3, 4 ≤ 8, and 0.6 ≤ n ≤ 1.4. The numerical experiments confirm the flow features and scales anticipated by the approximate boundary-layer solution.