A numerical study of the problem of heat transfer to the non-Newtonian power-law fluid over a vertical cone embedded in a porous medium has been investigated, taking into consideration the viscous dissipation effect. The governing equations describing the problem are transformed into a system of nonlinear ordinary differential equations, which is solved numerically using the Chebyshev spectral method. The effects of the power-law index and the viscous dissipation that is characterized by the local Gebhart number on the temperature profiles and the local Nusselt number are discussed.