The Mizuho Financial Group has announced it will be replacing the chief executive of its banking unit until April 2015.
Its move is an unexpected one, but comes just a few months after the Japanese lender admitted one of its subsidiaries had lent money to gangsters.
Yasuhiro Sato will retain a position on the bank's board and will continue in his role as chief executive of the parent company.
The current deputy president, Nobuhide Hayashi, will replace Mr Sato as the chief executive and president of Mizuho Bank.
A spokeswoman for the bank said that the change in leadership was part of a push to build a new structure within the organisation.
Japan's third-largest lender by market capitalisation is also considering a change in governance in a bid to bring it further into line with Western operating models.
The move will see it separate supervisory and business functions and appoint the board chairman from outside the bank.
By Asim Shah