The South Korean Foreign Ministry told reporters in Seoul the men were released Friday night, Yonhap News Agency reported.
The men and a Nigerian working with them were abducted from a construction site Monday. They were employed by Hyundai Heavy Industries.
Neither Hyundai nor the Foreign Ministry reported whether any ransom was paid to win the men's freedom.
"They are in good condition and say they have not been subjected to any harsh treatment while in captivity," Hyundai said in a statement.