Hypolimnas salmacis, the blue diadem, is a butterfly in the family Nymphalidae. It is found in Sierra Leone, Liberia, Ivory Coast, Ghana, Togo, Benin, Nigeria, Cameroon, Gabon, the Republic of the Congo, Angola, Equatorial Guinea, São Tomé and Príncipe, 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 , U. trinervis and species.