In this paper, natural convection heat transfer between pairs of elliptical cylinders having different elliptical ratios in blunt and slender situations was studied experimentally and numerically. Three pairs of elliptical cylinders having the same axes ratio of 2 and elliptical ratios of 0.662, 0.866 and 0.968 were cut using CNC wire-cut machining. The tests were carried out by keeping the inner cylinder at a constant heat flux while cooling the outer one. The effects of vertical eccentricity, horizontal eccentricity and angle of attack of the inner cylinder on natural convection for both blunt and slender situations of each pair were stated, Empirical correlation was deduced within acceptable uncertainty for the experimental results. A validated numerical CFD model was conducted with the case study to clarify the thermal behavior of air inside the elliptical annulus space between the two elliptical cylinders. Compatible and satisfactory to the conscience agreement was found in the comparison among present and corresponding previous works. In the vision of the comparison among the results of present work, it was found that the vertical eccentricity can enhance natural convection by about 15% than the concentric case, the horizontal eccentricity can enhance, natural convection by about 10% than concentric case and slender situation leads to about 30% - 40% enhancement in natural convection than the blunt situation for the same elliptical ratio.