The Kostur dialect (, Kosturski dijalekt), is a member of the Southwestern subgroup of the Southeastern group of dialects of the Macedonian language.Македонските дијалекти во Егејска Македонија: (Обид за класификација). Македонските дијалекти во Егејска Македонија: научен собир, Скопје 23-24 декември 1991. Скопје: МАНУ, 1994, стр. 23-60. This dialect is mainly spoken in and around the town of Kastoria, known locally in Macedonian as Kostur, and in the surrounding Korešta region, () which encompasses most of the area to the northwest of the town. The Kostur dialect is also partially spoken in Albania, most notably in Bilisht and the village of Vërnik (Vrabnik).According to some dialectologists the dialect of Vrabnik is a part from Kostur dialect only in general terms – see Христова, Евдокия. Българска реч от Албания. Говорът на село Връбник, Университетско издателство “Неофит Рилски”, Благоевград 2003, с. 10 [Hristova, Evdokia. Bulgarian speech from Albania. The dialect of the village Vrabnik, University Press "Neophyte Rilski", Blagoevgrad 2003, p. 10.] (in Bulgarian) The dialect is partially preserved among the ″people of Bulgarian origin in Mustafapaşa and Cemilköy, Turkey, descending from the village of Agios Antonios (Zhèrveni) in Kostur region (Aegean Macedonia)″.Koroloff, Larry Labro. Notes on the Dialect of Zhèrveni, Kostur Region, as Spoken by Their Descendants in Mustafapaşa and Cemilköy, Turkey. In: „Slověne“, №2, p. 112-116.
