Shape detection in digital images is one of the most effective subjects in image processing. This paper introduces a method for circle detection in digital images using genetic algorithm. Circle is expressed by a quadratic relation in coordinates screen. For circle detection, finding coefficients of this quadratic relation is the challenge. In the proposed method, three random points are selected on the edges of image. Because of each three points that do not locate on a straight line express a circle in coordinates screen, the quadratic relation coefficients of the circle are considered as the chromosome of genetic Algorithm. After finding the coefficients and drawing the circle, fitness function is calculated by computing amount of overlapping this circle with the edge of image. Then, the polynomial coefficients of new generations are generated by using crossover and mutation operators. Genetic algorithm continues until reaching the final conditions. Results of experiments on some of the images show that the proposed method can find circles on images. Increasing of the success rate in circle detection on image and exact detection of center and radius of circle are the contribution of this article in comparison with studied methods.