Hypolimnas salmacis, the Blue diadem, is a butterfly in the Nymphalidae family. It is found in Sierra Leone, Liberia, Ivory Coast, Ghana, Togo, Benin, Nigeria, Cameroon, Gabon, the Republic of Congo, Angola, Equatorial Guinea, Sao Tome and Principe, the DRC, Uganda, Sudan, Ethiopia, Kenya and Tanzania. The habitat consists of secondary forests and disturbed environments. Adult males mud-puddle. Both sexes feed from teak flowers. There are two female forms, one with blue and the other with an ochreous ground-colour. The larvae feed on Urera hypselodendron, U. trinervis and Fleurya species.