No independent verification of the rebels' statement was immediately available.
Video footage showed rebels inside the 18 sq km (7 square mile) facility in Orum al-Sughra among tanks and artillery they had seized. At least 18 troops loyal to President Bashar al-Assad were taken prisoner, opposition campaigners said.
A statement by the Aleppo Media Centre said at least 15 tanks were seized and that officers were among loyalist forces captured.
Mohammad Abdallah, an opposition campaigner in the north, said artillery stationed in the base has been used to bomb towns and villages in rural Aleppo and the neighbouring province of Idlib.
The base is situated 25 km (18 miles) west of Aleppo, Syria's commercial and industrial hub, about half-way between the city and the Turkish border.