The central city's forest protection department released a stump-tailed macaque or Macaca arctoides into the wild in Son Tra Nature Reserve.
Head of the mobile ranger team under the department Tran Minh Triet said a resident of Cam Le District handed over the monkey, weighing 0.7kg, to the team after a long captivity at home.
The animal is listed as vulnerable species in Viet Nam's Red Book by the International Union for Conservation of Nature (IUCN).
Last year, forest rangers and police in the city rescued 12 wild animals from a cafe in Cam Le District.
Some species of monkeys and birds, listed as endangered and critically endangered species in Viet Nam, are often kept in cafes or by families as pets.
The Son Tra Nature Reserve, known for its rich biodiversity, is home to 300 red-shanked doucs, a kind of langur that was declared endangered by the IUCN in 2013.
Son Tra –Ngu Hanh Son's Forest Protection Department filed a criminal case in March over the illegal killing of three red-shanked doucs (Pygathryx nemaeus) during a hunting trip in the reserve for money.
Last month, a red-shanked douc was found dead in the reserve with gunshot wounds.