The dusky large blue (Phengaris nausithous) is a species of butterfly in the family Lycaenidae. It is found in Armenia, Austria, Azerbaijan, Belarus, Bulgaria, Czech Republic, France, Georgia, Germany, Hungary, Kazakhstan, Moldova, Montenegro, The Netherlands, Poland, Romania, Russia, Serbia, Slovenia, Spain, Switzerland, and Ukraine. Life cycle of this species is strongly related to Sanguisorba officinalis (great burnet).