A numerical study on the natural convection heat transfer of slanted-pin fins mounted on a vertical wall has been conducted for the laminar flow regime. Assuming the air is the ideal gas, three-dimensional governing equations of flow and heat transfer was solved using the periodic boundary condition in the horizontal lateral direction with the SIMPLE algorithm. The effect of radiation heat transfer was considered using the discrete ordinate method based on the evidence of the code validation through a comparison with experimental data. The effects of the fin-inclination angle ranging from -45 degrees to +45 degrees and the aspect ratio of the rectangular-fin pins for 0.25-4.0 were examined for a modified Rayleigh number range of 5.2 x 10(10)-1.3 x 10(10) under constant heat flux conditions. For the positively-inclined fins, the enhancement of the heat transfer performance on the heated plate and fin-side surface was captured, which is similar to previous forced convection studies. For negative inclination angles, however, it was observed that the penetration of cold air from the quiescent region affects the heat transfer coefficient distribution on the top side of the fins in the vertical fin interspacing. As a result, in the present calculation, the negatively-inclined fins showed the best heat-transfer performance under a natural convection condition. Details on the buoyant-flow and heat transfer characteristics, such as the distributions of the local- and average-heat transfer coefficient, are quantitatively summarized. (C) 2018 Elsevier Ltd. All rights reserved.