As a result of the lichenological exploration in the Siirt Province of Turkey, the authors report 327 lichens, seven lichenicolous lichens and 27 lichenicolous fungi, representing 135 genera of Ascomycota. Thelidium pyrenophorum is new to Turkey, and 301 lichens and 26 lichenicolous fungi are new records for the Siirt Province. Furthermore, five lichens (Anema decipiens, Lecanora stenotropa, Peccania tiruncula, Sarcogyne arenosa, and Verrucaria bryoctona) have been found for the second time in Turkey. The localities where the taxa have been collected and their substrata are presented. Keywords: biodiversity, lichens, new records, southeastern Anatolia.