In this paper are presented the results of a numerical study on the chimney in a natural air-cooled electronic equipment casing. In order to promote the natural convective air-cooling capability, we have focused on about chimney effect by casing inclining. Moreover, we came up with assembling the chimneys on an inclined casing. For evaluating thermal behavior of inclination and chimney, experiments and numerical simulations have been carried out using a different material chimneys and a thin electronic equipment casing that has inlet and outlet in front-top side. As a result, we obtained the numerical simulation results for the thermal behavior inside the thin electronic casing, and it was in good agreement with experimental ones.