This study presents, for the first time, an automatic algorithm for surface rendering of a volume consisting of multi-axial cross sections. In computer graphics, although a medical volume is usually considered to consist of sequential parallel cross sections, multi-axial parallel sections that constitute a multi-axial volume have also been frequently used in recent clinical cases. Herein, a multi-axial volume is assumed to consist of multiple one-axial subvolumes occupying the same space. The discrete ray tracing algorithm that searches for only a hit voxel in a conventional one-axial volume is extended to search for multiple hit voxels in a multi-axial volume. Quadratic isosurfaces reconstructed from the hit voxels are used to approximate the object surface. The rendering results, applied to clinical cases to improve diagostic rates, indicate that 3D images obtained by applying our methods to multi-axial volumes are more clinically useful than those obtained from one-axial volumes.