Armathia island (Greek: Αρμάθια) is a Greek island belonging to the Dodecanese group in the eastern Aegean Sea. It is part of the municipality of Kasos. In the census of 1951 there were 8 recorded inhabitants but it has since become uninhabited. At its peak, it sustained a community of over 100 which were mainly involved in mining the rich deposits of gypsum intended for export. It is now a tourist destination for day-trippers from neighboring developed islands. The recently constructed observatory attracts wildlife observers.