The US State Department said Washington had secured assurances from Moscow the seven Russians would be "treated humanely" and in line with Russian law.
The departure of the seven Russians brings to 100 the number of prisoners who have been moved out of the Guantanamo facility since it opened in January 2002.
Eighty-eight have been sent back to their home countries for release and 12 transferred for continued detention in Saudi Arabia, Spain and Russia, the Pentagon said.
Neither the Pentagon nor the Russian government identified the prisoners, who were handed over to Russia on Saturday.
"The individuals were received by the relevant department of the Justice Ministry for further dispatch to a place of detention for preliminary investigations into their criminal cases," a Russian foreign ministry statement said.
One detainee's mother last year pleaded for the United States not to send her son back home, saying indefinite detention without trial by them was better than being in a Russian prison.
The Pentagon said in a statement the move followed "extensive discussions between our two governments".
"The decision to transfer or release a detainee is based on many factors, including whether the detainee is of further intelligence value to the United States and whether he poses a threat to the United States," the Pentagon said.
"The decision to transfer or release a detainee is based on many factors, including whether the detainee is of further intelligence value to the United States and whether he poses a threat to the United States"
The transfer of the seven Russian prisoners was the latest release of detainees from Guantanamo, where the United States continues to hold up to 800 non-US citizens caught in what President George Bush calls the global "war on terrorism". Most were caught in Afghanistan.
Russian officials have said the Russians detained in Afghanistan included Chechens detained fighting for the Taliban.
All but two of the prisoners are being held without charges and with no timetable for possible release.
The Pentagon last week sent a Danish national back to Denmark for release there.