Kostajnica can refer to: Kostajnica, Bosnia and Herzegovina (formerly Bosanska Kostajnica), a town on the right bank of river Una, in Bosnia Hrvatska Kostajnica, a town on the left bank of river Una, in Croatia Kostajnica, Doboj, a village near Doboj, Bosnia and Herzegovina Kostajnica, Konjic, a village near Konjic, Bosnia and Herzegovina See also Kostanjica, a village in the municipality of Kotor, Montenegro Koštanjica (Bar Municipality), Montenegro