Accurate measurement of vessel diameters on retinal images plays an important part in diagnosing cardiovascular diseases and early signs of certain systemic diseases, such as diabetes and hypertensio n. In this study we develop new method based on computer aided to determine the width of retinal blood vessels by analysing the color fundus image. Retinal vessel di ameter was measured based on blood vessel wall esti mating on the digital fundus image. We suggested a dependable and accurate technique to determine the diamete r (width) of retinal blood vessel based on suggested mask created to use specifically on measuring the b lood vessel diameter. The suggested system starts by removing the bifurcations and determine the width for each blood vessel segment. Suggested algorithm tested and gives accurate and promised results.