Vatnica (Serbo-Croatian: Ватница) was a župa (county) of the medieval Serbian state, Kingdom of Bosnia (after 1377), and the Duchy of Saint Sava (cca. 1468-83). It was located in a deep valley between Berkovići and Bileća (now eastern Bosnia and Herzegovina). It was first mentioned in the early 14th century as Vetanica (Ветаница), described as part of Travunija. It was transformed into the Ottoman nahiya of Fatnica (Фатница) in the 15th century.