The Britain-based Syrian Observatory for Human Right, which has a network of activists around the country, said government forces entered the prison at dawn, ending a siege that began in April 2013.
Lebanon's Al-Mayadeen and Al-Manar television stations, which are close to the Syrian government and have reporters in different parts of Syria, said government troops ended the siege.
The sprawling prison, which holds an estimated 4,000 inmates, has witnessed deadly clashes between government and opposition forces for the past year. Rebels repeatedly have barrelled suicide car bombs into the front gates and fought guards and troops holed up inside.
Aleppo has been carved into rebel- and government - controlled areas since opposition fighters launched an offencive in the north in mid-2012. The Syrian army appears intent on taking opposition-held parts of the country's major cities before the country's June presidential election.
Activists say more than 160,000 people have been killed since the Syrian conflict started in March 2011 as largely peaceful protests against President Bashar Assad's rule that deteriorated into civil war.