The 31-year-old and Cambodian-born Maddox, 5, flew from New Orleans to southern Vietnam's Ho Chi Minh City airport late on Wednesday night.
Jolie and Maddox were whisked into a car and driven to an undisclosed hotel, where they were to rest before Thursday's adoption ceremony.
The couple also have a biological child, Shiloh Nouvel, meaning the Vietnamese boy they are adopting would be their fourth child.
Adoption officials in Vietnam said following the adoption ceremony, Jolie will meet with U.S. consular officials, who have to approve the adoption before a passport can be issued for the youngster.
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