Heat transfer plays a major role in many processes in living systems. Natural convection in heat transport is one of the main species of heat transfer and is a mechanism, in which the fluid motion is not generated by any external source such as a fan, pump , etc. Its generated only by density differences in the fluid occurring due to temperature gradients. In the present research, natural convection heat transfer in an inclined rectangular cavity filled with air was presented . Top and bottom of vertical walls were adiabatic. The two horizontal walls of the opposing cavity have different temperature. The temperature of left wall was smaller than the right one. Dimension of the cavity H x L giving two dimensional flow .The hot and cold walls of the cavity were 60?C and 20?C respectively. Rayleigh numbers from 2.7x107 to 2.16 x108. Low Reynolds number of (k-?) model was used to make the flow very close to the turbulent flow . This study illustrate the effect of the degree of inclination, Rayleigh numbers in the flow field, the dimensions of content and average Nusselt numbers on the thermal heat load. ANSYS package was used to construct the results, such as temperature, velocity and pressure distribution. The local and average Nusselt numbers were also presented. From the constructed results, it was found there are good accordance between the results as compared to other researchers