This paper presents a two-passed registration method to register the pelvic CT and MR images. The geometrical relationship between CT and Mr images is determined by some uniquely selected internal landmarks which are all located on the coxal bone. Thus, it can be assumed to be a rigid transformation. In the first passed registration, the relative feature vectors, such as the normal vectors, such as the normal vectors of acetabular rim planes and the vector connecting two centroids of rims, are extracted and used for registration. The relative feature vectors determined based on the edge of acetabular rims are one of few features which can be observed on both CT and Mr images. The registration results based on the relative feature vectors are less influenced by the variation in the accuracy of the detection of absolute feature points. In the second passed registration, the corner points of sacrum are used to eliminate the distortion in z-directions. The least square error approximation is used to obtain the transformation matrix in both registration passes. In addition, a complete system is developed to provide clinicians with all image processing operations and visualization. For the visualization of fused data, 2D overlapping display and 3D transparent display are used to illustrate the correspondence of different structures, including bones and soft tissues. The fused images well demonstrate the information from two complementary modalities and are highly appreciated in clinical applications.