The International Monetary Fund is investigating whether its French director abused his power in an alleged relationship with a subordinate.
The IMF said the inquiry was instigated by a long-serving governing board member, Shakour Shaalan of Egypt.
In a statement, Mr Strauss-Khan said he was co-operating with the inquiry but denied abusing his power.
It comes as the world grapples with the worst financial crisis for decades.
The investigation is believed to centre on whether Mr Strauss-Kahn had a relationship with Piroska Nagy, until recently a senior IMF official.
It is to examine whether she got a larger severance package than would otherwise have been expected when she left the organisation in August.
The investigation is also looking at whether she was put under pressure to leave her job.
The IMF is currently receiving an increased number of requests for help from countries seeking to ease the effects of the global financial crisis.