The maximum intensity projection (MIP) is a useful tool to visualize 3D images. The processing time of the MIP depends on the number of voxels of the 3D data. Therefore, it is very difficult to realize the MIP of the 3D medical image in real time. In order to overcome the large amount of computation for the MIP, we have developed a hierarchical MIP method that can perform the first-step MIP with sub-sampled image. At second step, the lowresolution MIP image can be used to save the computation time of the full-resolution MIP image. The hierarchical MIP method was implemented and its computation complexity was analyzed.