Reliable and efficient Optic Disc (OD) localization is significant to automatic retinal image diagnosis. A fast automatic OD localization algorithm is presented. First, candidate OD locations are identified by gradient and intensity information. Then, by observation, the main vasculature are converged in OD region and spread along vertical direction. A template is used to locate the true OD center. The algorithm was tested on five publicly-available databases. The OD was successfully located in 1 514 images out of 1 540 images (98.3%). The averaged time for one STARE image is only 6.3 second. And the proposed method shows good robustness in both normal and diseased images.