An oval cut diamond having a girdle with elliptical or nearly elliptical outline, a crown which is above the girdle and has an octagonal table facet in the top section, and a pavilion which is below the girdle. The girdle has an aspect ratio (b/a) of 0.6 or more where a is the radius in the direction of the long axis and b is the radius in the direction of the short axis. A pair of pavilion main facets arranged opposite to each other with respect to the central axis have a crown main facet pair or a star facet pair respectively facing them across the girdle. Since these two pavilion main facets, two crown main facets or star facets, and the table facet have a common vertical plane in their facets, brightness of reflected light emerging above the table facet and the crown facets is enhanced.