Abstract: This study presented numerical prediction of natural convection heat transfer inside an inclined square cavity with perfectly conducting boundary conditions for the top and bottom walls. The modified Navier Stokes equations were solved using finite difference approach with uniform mesh resolution. The inclination angels were varied from 0° to 90° with 20° intervals. The results were presented in terms of streamlines and isotherms plots. The detailed heat transfer mechanism based on the average Nusselt number and inclination angles are presented. The effects of the boundary conditions on the sidewalls on the flow behavior are also demonstrated numerically.