Strandja or Strandha in Bulgarian and Yıldız or Istranca in Turkish is a mountain massif in southeastern Bulgaria and the European part of Turkey. The mountain is situated in the southeastern part of the Balkans between the plains of Thrace to the west, the lowlands near Burgas to the north, and the Black Sea to the east. Its highest peak is Mahya Dağı (1031 m a.s.l.) in Turkey, while the highest point on Bulgarian territory is Golyamo Gradishte (710 m a.s.l.). The total area of the massif is approximately 10,000 km 2 . Central and southern parts of the mountain are in Turkish territory, which comprises two-thirds of the area. Bosna Hill, which is part of Yıldız (Strandja) Mountain, and the northern parts of the massif are situated in Bulgaria. The climate of the area is considerably influenced by the Black Sea and is predominantly humid continental in the mountains and humid subtropical on the coast.Exploration of earthworm fauna of the Bulgarian part of Yıldız (Strandja) Mountain was begun by Černosvitov (1934). His work was continued by Plisko (1963) and Mihailova (1968). Recently, Uzunov (2010) and Szederjesi (2013) published new data from the region. The Turkish part of the mountain remains almost unexplored; only limited data have been registered by Szederjesi et al. (2014).The aim of the paper is to present new data on the earthworm fauna of Yıldız (Strandja) Mountain and to establish the first list of lumbricid biodiversity by analyzing the newly reported species together with literature data.Investigations were carried out during 3 different periods: September 2015, December 2015, and April 2016. Earthworms were collected using the diluted formaldehyde method (Raw, 1959), complemented with digging and hand-sorting. The combination of both methods creates a more complete sampling of species than the formalin method alone, which is not efficient in collecting species living in horizontal burrows. The specimens were killed in 70% ethanol and temporarily fixed in 4% formalin solution. After fixation in the formalin solution, they were transferred to 95% ethanol and finally into 75% ethanol.