Banking group Nomos is offering 21.8 million new shares to existing investors partly to fund the acquisition of a stake in rival Otkritie, the company said in a statement.
The shares would be worth 18 billion rubles ($559 million) at current prices, Reuters calculations estimated.
Otkritie and Nomos announced a deal in 2012 whereby Otkritie would take over Nomos. They later amended the plans in favor of Nomos taking a controlling stake in Otkritie.
Otkritie Financial Corp is owned by its directors, state bank VTB and Anatoly Chubais, an architect of Russia's post-Soviet privatizations.
Nomos said in a statement that it was launching a pre-emptive rights period for its shareholders to participate in the issue.
It will announce the results of the offering at the end of October.