Russia's Chief Military Prosecutor's Office said that there was no evidence of genocide against the Polish people and closed the "Katyn Case" in 2005.
"We will appeal the ruling, as during the investigation no relatives of those killed were recognized as victims. We request the Khamovnichesky Court of Moscow overturn the ruling to close the criminal case," lawyer Anna Stavitskaya said.
In 1940, over 20,000 Polish officers, taken prisoner during the 1939 partition of Poland by the Soviet Union and Nazi Germany, were executed in the Katyn forest, in prisons and other places by the NKVD, the forerunner of the KGB.
The Soviet Union accused Germany of executing the Polish prisoners. In 1990 Mikhail Gorbachev officially admitted that Soviet secret police had been responsible for the massacre.
Russian prosecutors earlier put the number of dead at 14,500.
