Abstract. Current automatic methods based on mid-sagittal plane to segment left and right human brain hemispheres in 3D magnetic resonance (MR) images simply use a planar surface. However, the two brain hemispheres, in fact, can not be separated by just a simple plane properly. A novel automatic method to segment left and right brain hemispheres in MR images is proposed in this paper, which is based on an extended shape bottlenecks algorithm and a fast and robust partial volume estimation approach. In this method, brain tissues firstly are extracted from the MR image of human head. Then the information potential map is generated, according to which a brain hemisphere mask with the same size of the original image is created. 10 simulated and 5 real T1-weighted MR images were used to evaluate this method, and much more accurate segmentation of human brain hemispheres was achieved comparing with the segmentation with mid-sagittal plane.