Ho Van Thanh left his home village with his son Ho Van Lang in 1971 after a mine blast killed his wife and two of his children. The Vietnam War was a Cold War-era conflict that claimed millions of military and civilian lives and left survivors traumatised.
Father(82) and son(41) survived by foraging for fruit, lived in a timber treehouse and wore loin cloths made from tree bark.
The authorities were alerted after locals searching for firewood spotted the men deep in the forest in Quang Ngai province's Tay Tra district.
A team was set up to look for the pair and found them after a five hour search.
The father could speak a little of the region's Cor language but the son only knew a few words.
The pair have been checked by doctors and a decision must now be made on how to reintegrate them to society.
Another son, Ho Van Tri, told Vietnamese newspaper VnExpress that he found them hiding out around two decades ago but could not convince them to return home with him.
The Vietnam war ended in 1975 with the fall of Saigon to North Vietnamese forces.