Unsteady natural convection inside a triangular cavity is studied. The cavity is filled with a saturated porous medium has a nonisothermal left inclined wall while the bottom surface is isothermally heated and the right inclined surface is isothermally cooled. Internal heat generation is also considered, which is dependent on the fluid temperature. The governing equations are solved numerically by the finite volume method. The Prandtl number of the fluid is chosen to be 0.7 (air) whereas the aspect ratio and the Rayleigh number are 0.5 and 10 5 , respectively. The effect of heat generation on the fluid flow and heat transfer is presented in terms of streamlines and isotherms. The rate of heat transfer through the three surfaces of the enclosure is also presented.