Authorities in Dak Glong District said Saturday that the bodies of the three men, aged 29-41, had been found by local people the previous afternoon.
They have been identified as residents of the district’s Quang Hoa Commune.
The police said the trio might have entered the gold mine to look for scraps usually left behind by gold miners.
They are thought to have suffocated after descending 50m due to a lack of oxygen and eventually succumbing.
The mine lies deep inside a forest managed by the local Quang Son Forestry Co. Ltd.
The area does not get phone signals and has many illegal gold mines.