The purpose of the present study is to analyze numerically the developing mixed convection in a vertical parallel-plate channel partially filled with porous medium. The SIMPLEC algorithm combining the techniques of ADI and SOR is used in this study. The diffusion and convection are handled by a hybrid scheme. The non-Darcy model, which includes inertia effect, boundary friction effect and convection, is used in the momentum equations for the porous medium layer. The velocity and temperature distributions, local Nusselt number (Nu(x)), local friction coefficient (C-f), pressure drop and entrance length in a vertical parallel-plate channel partially filled with porous medium are obtained under various parameters, such as different thickness of porous medium (Rs), Darcy number (Da), Grashof number (Gr). The numerical results of this investigation show that (a) the local Nusselt number increases as Rs decreases and Da and Gr increase; (b) the local friction coefficient increases as Da and Gr increase; and (c) the pressure drop in the parallel-plate channel increases as Rr increases and Da decreases. There is a minimum non-zero local friction coefficient where the thickness of the porous medium is about 0.2. Hydrodynamic entrance length is shorter as the value of Rs is increased, and is longer as the values of Da and Gr are increased. Thermal entrance becomes longer as the values of Rs and Da increase and shorter as the values of Gr increase.