In this paper problem of edge detection in digital images is considered. Three methods of edge detection based on mathematical morphology algorithm were applied on two sets (Brain and Chest) CT images. 3×3 filter for first method, 5×5 filter for second method and 7×7 filter for third method under MATLAB programming environment. The results of above mentioned methods are subjectively evaluated. The results show these methods are more efficient and suitable for medical image which can be used for different other applications.