Nguyen Thi Thanh Trang, the 36-year-old manager of the orphanage in the capital's Bo De pagoda, was taken into custody Sunday pending a police probe into the trafficking of a one-year-old boy for $1,700, Tuoi Tre newspaper said.
Another woman, Pham Thi Nguyet, 35, was also arrested while three others have been questioned over the same allegation, the report added without clarifying their roles at the pagoda.
The Bo De Pagoda in Hanoi is renowned for its orphanage where dozens of abandoned children are cared for, including the disabled -- from teenagers with Down Syndrome to blind babies.
The boy, who was believed to have been left at the pagoda's entrance at birth, disappeared suddenly "without reason", the report said, adding complaints led to the police investigation.
Officers discovered that the boy was "in fact trafficked" in exchange for $1,700.
The probe is ongoing to identify whether there were any other similar cases involving the orphans.
As of mid-July the pagoda was home to 145 orphaned, abandoned or disabled children as well as elderly people in need of care, Tuoi Tre said.