Kostajnica (Serbian Cyrillic: Коstajnica), is a town and municipality in northern Bosnia and Herzegovina, part of the Republika Srpska entity. It is situated in the part of the Кrajina region. The municipality was created from part of the pre-war municipality of Novi Grad. It is located across the Una from Hrvatska Kostajnica, Croatia.
Passport stamp bearing just the name Kostajnica.
During the Bosnian War, it was renamed to Srpska Kostajnica (Српска Костајница). After that, name of the town was changed to Kostajnica.
In the 1991 census, Kostajnica was part of the Novi Grad municipality, and its population numbered 3,768 people, including:
Note: The vast majority of those who declared as Muslims by nationality in 1991 have considered themselves Bosniaks since the Bosnian War, as before the 1910s.
From 1929 to 1941, Bosanska Kostajnica was part of the Vrbas Banovina of the Kingdom of Yugoslavia.
Coordinates: 45°13′N 16°32′E / 45.217°N 16.533°E