Entropy generation due to natural convection in isosceles triangular enclosures with inclination angles (phi) filled with a fluid-saturated porous medium has been studied numerically. The enclosure has different inclination angles and it is non-uniformly heated from one side. The finite difference technique was adopted to solve the governing equations of this natural convection problem. Then, entropy generation due to heat transfer irreversibility (HTI) and fluid friction irreversibility (FFI) was calculated from its definition using dependent variables of velocities and temperature fields. Calculations were performed for different Rayleigh numbers Ra in the range of 100 <= Ra <= 1000 and inclination angle, 0 degrees <= phi <= 180 degrees. It is found that both inclination angles and Rayleigh numbers make important effect on natural convection heat transfer, fluid flow and entropy generation. The highest entropy generation due to HTI and FFI and stream function are observed at phi = 90 degrees. Multiple cells were formed at this angle. Streamlines, isotherms and entropy contours are symmetric inside the enclosure for both phi = 0 degrees and phi = 180 degrees. (C) 2008 Elsevier Ltd. All rights reserved.