In this study, the heat transfer by natural convection From partially open cavities with one wall heated was investigated numerically. The aim of this Study was the steady state investigation or the natural convection heat transfer inside the cavity under uniform heat fluxes (q ''). different opening ratios (OR), tilt angles (0) and cavity aspect ratios (AR) for top and center opening positions. For this purpose, the equations of conservation of mass, momentum and energy were solved using adequate boundary conditions by means of the PHOENICS code. According to the results obtained, the average heat transfer coefficient increases and the average wall temperature decreases, with the increase in opening ratio and decrease in the tilt angle. Best heat transfer was obtained with the maximum aspect ratio for opening ratio of 0.75 and tilt angle or -10 degrees.