The amnesty is believed to include members of the banned Muslim Brothers, the Communist Action League and other parties. Some of the detainees are said to be Lebanese.
"This is an encouraging first step towards the release of all political prisoners in the country," a spokesman for Amnesty International said.
Amnesty estimated that Syria had between 1,000 and 1,500 political prisoners before the releases were announced.
Since inheriting the presidency after the death in June of his father, Bashar, 35, has been pushing for a degree of political and economic reform in what was widely regarded as a hidebound police state.
The release of prisoners commemorated November 16, 1970, when the "Corrective Movement" purged its rivals in the Ba'ath party and Hafez al-Assad seized the presidency.
Patrick Seale, biographer of the late leader, said yesterday: "Dr Bashar is anxious to improve Syria's human rights image. Shortly after taking over he set up a committee to visit jails and examine cases.
"He also wants to heal the wounds of the past, especially with the Muslim Brothers."
Many of the Brothers were arrested in the 1980s during a suppression which included the 1982 massacre at the town of Hama. Under Syrian law, membership of the Muslim Brothers is still a capital crime.
The release of about 100 Lebanese political prisoners is also seen as a goodwill gesture towards Lebanon, where Syria maintains 20,000 or more troops.
Opposition to this military presence has been growing recently. Many Lebanese see no justification for it now that the Israeli army has withdrawn from the south.