Voters in some regions will choose governors and others will select regional parliaments on Sunday.
But the main opposition Democratic Coalition has been allowed to stand in just one region, Kostroma.
The coalition includes the parties of murdered politician, Boris Nemtsov, and protest leader, Alexei Navalny.
Navalny cannot run for office as he is serving a suspended prison sentence in an embezzlement case that he argues was fabricated.
The Duma has been stripped of any real opposition under President Vladimir Putin.
The Democratic Coalition's campaign has not been easy - with no media coverage and accusations that they are working for the US, reports the BBC's Sarah Rainsford in Kostroma, north-east of Moscow.
"They tried to damage my campaign in many ways - with lies, with propaganda, with provocateurs with police," said Ilya Yashin, the main coalition candidate in Kostroma.
"This year they killed my friends. Another of my friends is in prison. He was a chief of staff of my campaign in the first period.
"We must keep fighting because you know, it's a question about the future of our country. If we will stop that means they win."
Russia's main opposition groups combined forces in April, nearly two months after the murder of Mr Nemtsov, who was shot dead while walking with his girlfriend near the Kremlin.
The coalition, campaigning under Mr Nemtsov's party name Parnas, hopes the the regional elections will be a springboard for the 2016 national parliamentary vote.
The second opposition candidate standing in Kostroma is Vladimir Andreichenko.
Russia is entering the final hours of campaigning for regional elections widely seen as a test ahead of parliamentary polls in a year's time.