Troops and allied militiamen retook the Hama province villages of Aqareb and Al-Mabujeh a day after the jihadist assault, the Syrian Observatory for Human Rights said.
The IS attack killed 25 civilians, including five children, and 27 pro-government fighters, the Britain-based monitor said.
At least three of the civilians, a man and his two children, were executed with knives, it added.
The Observatory reported 10 IS fighters killed in the assault, which began at dawn on Thursday and saw jihadists briefly seize all of Aqareb and parts of Al-Mabujeh.
State news agency SANA said 52 people had been killed, among them 15 children, adding that many of the dead had been beheaded and mutilated.
The two villages are home to members of several religious minority sects, and Al-Mabujeh has been targeted by IS before.
In March 2015, the group killed dozens of people and kidnapped some 50 civilians in an attack there.
IS is on the defensive across most of the territory it still holds in Syria, with an alliance of Kurdish and Arab fighters pressing towards its most important bastion, Raqa in the north.
The army is also battling the jihadist group in the eastern part of Aleppo province.
The Observatory said at least 22 government troops and allied militiamen and 40 IS fighters had been killed in clashes in the area in the past 24 hours.
And in the eastern city of Deir Ezzor, which is largely under IS control, jihadist shelling of a government-held neighbourhood killed at least 14 people, the monitor said.
A dozen people were also wounded by the artillery fire, which hit a wedding party.
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