Abstract: To overcome the difficulty caused by intensity in homogeneity in the segmentation of magnetic resonance (MR) images,this paper presents a new multiphase level set model for segmentation of brain MR images. The proposed model utilizes local image intensities,which enables it to cope with intensity inhomogeneity. The proposed model can extract brain white matter (WM),gray matter (GM) and cerebrospinal fluid (CSF) simultaneously and provide a smooth contour surface. Comparisons of 2D and 3D segmentation demonstrate the model's effectiveness.