Ostabarret (Basque: Oztibarre, Spanish: Ostabares) is a central region of the traditional province of Basse-Navarre in the far south of France.
It is hilly, open country, characterized by low mountains and round hills between 160 and 650 metres in elevation.
The region is first mentioned as the terra Ostabaressii in a document of the twelfth century.
The forms Ostabarea (1312) and Hosta-Barisium (1351) are attested, while the Gascon Rolls use Ostaberesium (1361).
The dialect was classified by Louis Lucien Bonaparte as Lower Navarrese in 1869.