We propose a new approach for detecting ellipses. The approach is based on the geometrical property that five points on an ellipse can determine the parameters of the ellipse, and the symmetry of ellipses is used to obtain these points. Using symmetry, we classify the edge points in an input image into several subimages. Ellipses with different symmetric axes will lie in different subimages. In each subimage, symmetry is applied again to obtain those sets of five points that possibly lie on the same ellipse. Finally, using geometrical properties and the Hough transform, we extract all ellipses in an input image successfully. The proposed method can detect partially occluded ellipses. Experimental results show that the proposed method is fast and robust.