In this paper segmentation of benign and malignant masses found on mammograms were segmented. After adding low valued pixels outside of mammogram, Chan-Vese active contour algorithm with a new stopping criteria was implemented. As a result, lacking segmentation was prevented. Experiments were made on 60 mammograms which had masses with different shape, size and visibility taken from Digital Database for Screening Mammography(DDSM). Proposed method had a Area Overlap Ratio of % 75.1.