Al-Qaeda and other Islamist brigades managed to take control of the major part of the town serving as the capital of province Idlib on Saturday.
The strategically important town is located on the road connecting Syria's second city of Aleppo with the coastal city of Latakia.
Earlier, the so-called "Army of Conquest" seized the city of Idlib.
The insurgents began their attack on Jisr al-Shughour on Thursday.
This is the town where Hafez al-Assad, former Syrian president and Bashar Assad's father, was born.