"Our brave armed forces have full control over Yabroud in Damascus province and are combing through the town and removing explosive devices placed by terrorists," state television said, citing a military source.
Opposition sources said civilians and activists from the town had fled across the nearby border into Lebanon overnight before Yabroud fell.
The loss of the town will be a symbolic and practical blow for the opposition, AFP reported.
It has been a rebel stronghold since early in the uprising that began in March 2011 and has proved a key strategic prize because of its proximity to the Lebanese border, across which weapons and fighters can be smuggled.
It also lies on the important highway that connects Damascus to Syria's third city Homs.
Lebanon's Shiite movement Hezbollah, which has dispatched its well-trained fighters to bolster the government's forces, is believed to have played a key role in the capture of Yabroud.