Police in Hanoi arrested a married couple on Friday, after they discovered the bodies of 12 red-listed douc langurs along with 2,400 packets of tobacco in their car.
Police said the car, driven by Luan Trung Thanh, 38, was stopped for inspection while travelling from the Central Highlands province of Dak Lak to the northern province of Cao Bang.
Thanh's wife, 30-year-old Nguyen Thi Tuyet, was also in the car.
The bodies of the monkeys, which were red-listed in Vietnam, were found dried.
Police say they suspect that the couple intended to smuggle the creatures into neighboring countries for sale on the black market.
Their investigation continues to be underway.