Located in the southwest of the country, bordering on Covalima, Bobonaro and Ermera districts to the west, Aileu to the north and Manufahi to the east. The Timor Sea (Tasi Feto) coast forms the southern border to the district.
It has a population of 59,175 inhabitants (Census 2010) and an area of 797 km2. The capital of the district is also named Ainaro.
The district combines several contrasting topographic features, climactic and soil conditions.
Towards the north, in Hatobuilico sub-district, Mount Ramelau (2,963 metres) forms the highest peak in the country. These upper reaches constitute Timor's water tower and are among the potentially richest and most diverse agricultural areas in the country, suitable for pasture, inland fisheries, timberand livestock breeding. The spectacular panoramic mountain scenery in this area has also great tourist potential.
Towards the south of the district and the coast, the terrain descends into lowlands - gradually beginning to resemble parkland savannah.