Dozens of others were either taken prisoner or went missing when the Al-Nusra Front and a coalition of mostly Islamist groups captured the Abu Duhur military airport yesterday, the Syrian Observatory for Human Rights said.
"There were at least 56 (soldiers) killed yesterday and at least 40 taken prisoner, and dozens more are missing," the Observatory's Rami Abdel Rahman told AFP.
"Some soldiers were executed," said the head of the Britain-based group that relies on a network of sources on the ground in Syria for its information.
Rebels also uploaded images of helicopters and planes abandoned on the tarmac, with militants posing seated on one of the aircraft making V-for-victory signs.
The fate of other missing soldiers remained unclear, said Abdel Rahman, who added that the entire northwestern province of Idlib was under the control of Al-Nusra Front and other rebel groups.
The insurgents had taken advantage of an intense sandstorm that blanketed much of the Middle East on Tuesday evening to seize the airbase, the Observatory said.
It has been at war with different rebel groups for the past four and a half years, in a conflict that has killed at least 240,000 people and forced millions more to flee abroad.
