Nigeria's Securities and Exchange Commission (SEC) has fired the director-general of the Nigerian Stock Exchange, Ndi Okereke-Onyuike, and suspended its chairman.
The move is being seen as an effort to restore investor confidence following growing fears over governance issues.
The action was taken by SEC head Arunma Oteh who took office at the beginning of 2010 promising tougher regulation.
The SEC has named ex-Deloitte executive Emmanuel Ikazoboh as its new chief.
The former chief executive of Deloitte in West and Central Africa will now be responsible for managing sub-Saharan Africa's second-biggest stock exchange for a caretaker period.
The SEC sacked Ms Okereke-Onyuike and suspended the stock exchange's president, Nigerian businessman Aliko Dangote.
Brokers arriving for work on Thursday were met by armed police who were there to ensure there was no challenge to the SEC directive.
"This strong move by the SEC to get a grip of the situation and try to resolve the leadership crisis can only improve investor confidence, especially if the proposed interim administrator organises elections in a timely manner," said Kayode Akindele, a director at financial advisory firm Greengate Strategic Partners.
Last month financial regulator Arunma Oteh said she would bring 260 organisations and individuals to a special tribunal over alleged abuses in the country's stock markets.
Nigeria's banking crisis last year exposed widespread abuses in the capital markets.
As Nigeria's banks came close to collapse, it became clear that lax regulation and inadequate surveillance of stockbrokers was a major problem.