Kostajnica (Serbian Cyrillic: Коstajnica), is a town and municipality in northern Republika Srpska and Bosnia and Herzegovina. 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 1910s.
Coordinates: 45°13′N 16°32′E / 45.217°N 16.533°E