Aileu is an administrative district of East Timor. It has a population of 37,926 (Census 2004) and an area of 729 km². The capital of the district is also named Aileu. The subdistricts are Aileu, Laulara, Lequidoe and Remexio.
Aileu is in the northwestern part of East Timor and is one of only two landlocked districts, the other being Ermera. It borders Dili to the north, Manatuto to the east, Manufahi to the southeast, Ainaro to the south, Ermera to the west, and Liquiçá to the northwest. It was formerly part of the district of Dili but was split in the final years of Portuguese administration.