A rear aperture sight for use in conjunction with a front sight post sight on a rifle. The front sight post has a horizontal top edge and vertical side edges. The rear aperture sight comprises a rear sight adapted to be mounted on the rifle. The rear sight has a horizontally elongated aperture formed therein having height and width dimensions. The width dimension is greater than the height dimension. The height dimension is of such a value that the aperture is adapted to cause the horizontal top edge of the front sight post and a horizontal edge of a target to be sharply focused. The width dimension is of such a value that the aperture is adapted to permit a sufficient amount of light to pass through the aperture so that the front sight post and the target are bright.