Usage of Computer Aided Diagnostic (CAD) systems is increasing rapidly. Blood vessel segmentation on retinal fundus images could be used as a CAD system for diagnosis of various retinal diseases. In this paper, blood vessels are segmented on retinal fundus images. Firstly, Gabor filter and morphological top-hat transform are applied after preprocessing step in order to enhance blood vessels. Afterward, we performed p-tile thresholding method to obtain binary vessel image. At the last step a post processing method is applied to increase accuracy. In order to test the developed system, the images obtained from STARE and DRIVE databases are used. Finally, 94.02% of accuracy for STARE database and 94.59% of accuracy for DRIVE database are obtained as a result, which is promising.