Holographic interferometry has been successfully applied quantitatively to visualize shock wave phenomena. This paper will demonstrate that this flow visualization technique is more effective in observing three-dimensional shock wave reflection over cones than other conventional flow visualization techniques.It is well documented that, in a two-dimensional shock wave reflection over a wedge, regular reflection or Mach reflection occurs according to the shock Mach number and the wedge angle. When a shock wave reflects at the surface of a cone which has an attack angle, these two reflections can both appear simultaneously because of the difference of incidence angle. Depending on the attack angle of the cone, either regular or Mach reflection occurs. However, very little is known of the three-dimensional shock transition from regular to Mach reflection or vise versa. From a physical point of view, it is important to determine the transitional angle between regular and Mach reflection by using a holographic method. In this paper, a shock wave reflected from a cone at an angle of attack was visualized quantitatively by using double exposure holographic interferometry and diffuse holographic interferometry.