Ainaro is one of 13 administrative districts of East Timor, in the southwest part of the country. It has a population of 53,629 (census 2004) and an area of 797 km². Its capital is the city of Ainaro, a small mountain town.
The district is identical to that of the same in Portuguese Timor, with the following exceptions: during the Indonesian occupation, the subdistrict of Turiscai became part of Manufahi from Ainaro, and the subdistrict of Hatudo became part of Ainaro in exchange. The suco of Mape-Zumalai became part of Cova-Lima in 2003.
The district borders the districts of Aileu to the north, Manufahi to the south, Cova-Lima to the southwest, Bobonaro to the west, and Ermera to the northwest. The subdistricts of Ainaro now are Ainaro, Hatudo, Hatu Builico, and Maubisse.
Ainaro has a great abundance of rivers and fertile terrain for agriculture. It has a coastal area, on the Timor Sea, but also mountainous zones, including the highest point in East Timor, Mount Ramelau (2,960 m), also known as Tatamailau, which lies near the border with Ermera. Historically, Ainaro played an important role during the brutal Indonesian occupation of East Timor, providing shelter for the mountain-based guerrilla resistance army. Former guerrilla leader and current President Xanana Gusmão spent many years directing the resistance from Ainaro.
In addition to the official languages of Tetum and Portuguese, a large number of inhabitants of Ainaro speak the Malayo-Polynesian language Mambai. The inhabitants include catholics, protestants, and muslims living side by side.