The two sisters, named Be and Em, were confiscated by authorities from a man who admitted catching them in a cardamom field with a plan to sell them, the Four Paws organization said.
Vietnam is a major hub for the illegal trade in wild animals, and bears are kept to drain the bile from their gall bladders for use in traditional medicine.
The rescued cubs have been taken to a sanctuary in Vietnam run by Four Paws, where they will be reared and spend the rest of their lives.
They cannot be returned to nature because there are no safe places for bears in Vietnam and no projects to reintroduce them to the wild.
"At the moment they mostly eat, play, and sleep but we can already see their individual personalities showing," Emily Lloyd, Animal Manager at the sanctuary, said in the Four Paws statement.
"Be is very playful and confident, while Em for now is more reserved but nonetheless curious."
Four Paws said the sanctuary has hand-raised five bears rescued from similar circumstances in recent years.
Vietnam has passed laws to try to curb the wildlife trade but enforcement is patchy and Four Paws said the bear bile business was "flourishing."