Oly Ilunga, who resigned as DR Congo health minister last month, was questioned on Tuesday as part of an enquiry into the use of public funds earmarked to tackle the Ebola epidemic, a judicial source said.
The former minister's evidence was heard by the attorney general "and he then left freely", the source told AFP.
Three of the minister's former co-workers, including a doctor, were held in custody the source added, confirming a report by the Top Congo radio station.
The hearings were part of a preliminary inquiry "into the management of substantial funds provided by the government for the battle against the Ebola virus," which has claimed almost 2,000 lives, another source said.
Ilunga resigned last month, citing his removal as the head of the Democratic Republic of Congo's Ebola response team and concerns over a proposed "experiment" with a new, unlicensed vaccine.
Nearly 170,000 people have been given an Ebola vaccine manufactured by German pharma giant Merck since the outbreak started in Democratic Republic of Congo a year ago.
The World Health Organization (WHO) has been pushing for the introduction of a second vaccine produced by US company Johnson & Johnson, but the health ministry under Ilunga has resisted such a move, citing the risks of introducing a new product in communities where mistrust of Ebola responders is already high.
The Merck vaccine is tested but unlicensed, while the Johnson & Johnson drug is still in the trial investigation stage.
The vast central African nation's new pointman on Ebola, Jean-Jacques Muyembe, told reporters on Tuesday that "we now have the situation on the ground under control."
"There is great hope that thing will get a lot better in the days to come, he added, thanking China for 60 tonnes of medical equipment to tackle the problem.
Since August last year, Ebola has killed more than 1,900 people in the DR Congo, the second-biggest epidemic since more than 11,300 people died in Liberia, Guinea and Sierra Leone between 2014 and 2016.