A floristic study of the Yildiz Mountains Biosphere Project was undertaken between May and October 2009. The project area is located in the north-eastern part of European Turkey, within flora square A1-A2 (E) (Kirklareli), and covers about 1300 km(2). The list of vascular plants was prepared mainly based on specimens collected during the flora surveys of the Project and supplemented by earlier gathered specimens kept in the EDTU, ISTE, and ISTO herbaria. In the project area 1315 taxa, belonging to 505 genera and 113 families, were determined. Among these, 18 taxa are Pteridophytes, 4 Gymnospermae, 1035 Dicotyledones, and 258 Monocotyledones, The 3 largest families are Compositae (153 taxa; 11.5%), Leguminosae (119 taxa; 9.1%), and Graminae (102 taxa; 7.9%). The richest genus is Trifolium (62 taxa). Among the more significant finds of this floristic survey of the research area are 15 endemic taxa for Turkey and 29 taxa that are not recorded in the Asiatic part of Turkey, a new species for plant science (Allium rumelicum M.Kocyigit & N.Ozhatay), 3 new records for Turkey (Allium saxatile M.Bieb., Anthoxanthum aristatum Boiss., and Elatine triandra Schkuhr), and 8 new records for European Turkey.