The nuns went missing in December after Islamist fighters took the ancient quarter of the Christian town of Maaloula, north of Damascus.
After being held in the Greek Orthodox monastery of Mar Thecla in Maaloula, they were reportedly moved to the town of Yabroud, 13 miles to the north, which is now the focus of a government military operation.
Syrian Greek Orthodox Bishop, Louka al-Khoury, welcomed the news, saying: "What the Syrian army achieved in Yabroud facilitated this process."
It was unclear exactly who had held the nuns and why they had been released now.
In December, the nuns appeared in a video saying they were in good health.
Syria's Christians have tried to stay on the sidelines of the country's three-year-old-conflict, which has killed more than 140,000 and become increasingly sectarian. The rise of hardline Islamists among the overwhelmingly Sunni Muslim opposition has alarmed many.