The militants, mostly from the al-Qaeda-linked Nusra Front, withdrew from the Armenian town near the Turkish border on Saturday.
The withdrawal came after tanks of the Syrian army took position in the nearby villages signaling an impending attack.
The so-called Syrian Observatory for Human Rights said the militants left behind “only a small number" of their men.
The militants are said to have pulled back to their strongholds in the rural mountainous region of Jabal al-Akrad.
Kasab’s liberation is strategically important as the town is located near the only border crossing with Turkey in the Latakia province.
The militants took control of the mostly Armenian-populated town last March.
Meanwhile, units of the Syrian army made major gains in their battles against militants elsewhere in the country.
The Britain-based observatory said on Friday that at least 130,000 people have been forced out of their homes since late April.
The group added that Takfiri militants of the Islamic State of Iraq and the Levant (ISIL) were preventing food and medical supplies from reaching some neighborhoods of Deir al-Zour in eastern Syria.
Syria has been gripped by deadly violence since March 2011. Over 160,000 people have reportedly been killed and millions displaced due to the violence fueled by the foreign-backed militants.
The Western powers and their regional allies -- especially Qatar, Saudi Arabia and Turkey -- are supporting the militants operating inside Syria.
NTJ/HH