In this study, the authors present a simple method to estimate intrinsic and extrinsic parameters of the camera for roundabout traffic scenes. Unlike many previous works on camera calibration for roadway scenes by using parallel lines, the proposed work addresses camera calibration for roundabout scenes by using a circle. The proposed method can estimate focal length, pan angle, tilt angle and camera height by matching the ellipse equation extracted from an image with the perspectivetransformed equation of the corresponding real-world circle. This method requires only one image for camera calibration. The method is validated with real-world roundabout traffic scenes and the calibration results are reasonably accurate compared with ground truth measurements.