Police in Georgievsk, the Stavropol Territory, said they planned to open an inquiry into the incident after unidentified people broke the monument on the grave of Taisiya Solzhenitsyna.
She died of tuberculosis at the age of 49 on this day in 1944, two weeks after her brother's death, and was buried together with him.
Alexander Solzhenitsyn, 87, a Soviet-era dissident writer whose work exposed the horrors of the Stalinist labor camps, was imprisoned, stripped of his citizenship, and expelled from the Soviet Union in 1974 following the publication of his seminal work The Gulag Archipelago.
He returned to Russia in 1994 after 20 years of exile in the United States only to find his mother's grave gone.
It was re-discovered in spring 2006 at the Georgievsk cemetery where the St. George's Church is currently being built sponsored by Solzhenitsyn, among others.
Solzhenitsyn had to pay a high price for his opposition to the regime. The writer was imprisoned by Stalin for eight years for a frontline letter he wrote to a friend critical of the Soviet leader, but later enjoyed acclaim with the publication of his first book, A Day in the Life of Ivan Denisovich, under a cultural thaw initiated by Stalin's successor, Nikita Khrushchev.
Mikhail Gorbachev restored Solzhenitsyn's citizenship in 1990 and later dropped treason charges against him.