German War Graves Commission says it has unearthed remains of 800 German soldiers killed in World War II.
This was done during building work in the south-western Russian city of Volgograd, the commission said.
The discovery in the once fiercely-contested city, previously known as Stalingrad, was made while water pipes were being laid, the commission said.
The commission added that it will be problematic to perform Full excavation due to parts of the grave which located beneath a housing development.
Recalling the war, the victory of Soviet troops at the Battle of Stalingrad is considered a major turning point in the war.
In the winter of 1942/43, it is estimated that some 700,000 soldiers and civilians died on both sides.
Some historians believe more than one million people died during the battle, with many of them freezing to death in below-zero temperatures. Many are still officially missing.
The bones from the mass grave are believed to have belonged to soldiers, who died in the winter months of 1942/43, according to the association.
The association has been working with Russian authorities in the area for some 25 years.
If remains are clearly identified with the help of identifying features and historical documents, family members are contacted.
The remains are then reburied in official military cemeteries such as Rossoshka, about 40 kilometres outside Volgograd.