X-ray computed tomography (CT) is widely used as a nondestructive inspection technique in the medical, security, and industrial fields. The authors propose a method of visualizing the internal defect structure of an aluminum die-cast part imaged by 3D X-ray CT for industrial use using mixed reality (MR). In the proposed method, the data acquired by X-ray CT is reconstructed three-dimensionally using surface rendering and cross-sectional representation, and integrated into an MR environment using a spatial reality display and motion capture. The spatial reality display’s eye-tracking function enables the provision of 3D images according to the user’s viewpoint, and by using motion capture, it is possible to rotate and move objects using hand gestures, enabling intuitive interaction. As a result of the experiment, this system made it possible to intuitively understand the internal structure, which was difficult with conventional visualization methods using a fixed viewpoint. In addition, it became possible to understand the space more than with 2D visualization methods by segmenting and grasping defects and voids in three dimensions. The proposed visualization method using MR is expected to contribute to the nondestructive inspection of industrial products with complex shapes, such as automobile parts and precision equipment, in the future.