A method and a system for localizing at least one circular object in a video frame captured by an image capture unit are disclosed. The method includes the steps of: A. performing edge detection to obtain a plurality of image edge points in the video frame; B. extracting a contour set of image contours by linking neighboring edge points; C. generating a plurality of circle samples from the extracted contour set by a structural sampling process; and D. localizing the at least one circular object from the generated circle samples by calculating a respective fitness score for each of the circle samples to measure the supporting evidence of the image edge points on a neighborhood of each of the circle samples, and by choosing the circle sample(s) whose fitness score(s) is/are greater than a threshold value as the circular object(s) found in the video frame.