The grave contained 65 bodies, mostly soldiers, which were piled on top of each other, Arabic-language Syria Now news website reported on Wednesday.
The bodies of a woman and a child were among the corpses which showed marks of torture with some beheaded.
The victims are believed to have been executed by Daesh (ISIS / ISIL) militants after the Takfiri militant group in May 2015 seized the ancient city, which hosted some of the most well-preserved ruins of antiquity.
Daesh destroyed temples, burial towers and the Arch of Triumph at the desert oasis dating back more than 2,000 years. It also looted graves and used the amphitheater of the city to stage killings.
According to reports, Daesh committed a massacre in Palmyra on May 24, 2015, leaving at least 400 people dead, most of them women, children and elderly people.
On April 1, a mass grave was uncovered by Syrian forces in the northeastern parts of Palmyra. The grave contained bodies of 42 people, including women and children, who were killed by Daesh terrorists.
The Syrian army, backed by popular forces and a wave of Russian air strikes, retook the ancient city of Palmyra from Daesh on March 27 following weeks of military operations against the Takfiri group.
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