Rasmiya Awad was captured alongside her husband and daughter-in-law in a raid on a container near Syria’s Azaz.
The number of people with family ties to al-Baghdadi who have been caught by Turkey “is close to reaching double digits”, Erdogan added.
The Turkish leader’s comments were his second effort in as many days to publicise his country’s push to catch Islamic State of Iraq and the Levant (ISIL or ISIS) members who were close to al-Baghdadi.
“All of al-Baghdadi’s inner circle is mostly targeting our country and these people are looking for ways to settle in our country or to come to our country,” Erdogan told reporters.
He and Turkish officials said on Wednesday that Turkish police detained one of al-Baghdadi’s wives and a daughter last year.
A Turkish official told The Associated Press they were among a group of 11 ISIL suspects detained in a raid in southern Turkey on June 2, 2018.
Police identified the wife as Asma Fawzi Muhammad al-Qubaysi. The official said she was the first wife of al-Baghdadi, who is known to have four wives.
A subsequent DNA test confirmed a suspect who identified herself as Leila Jabeer was al-Baghdadi’s daughter, the official said.
Turkish authorities said they captured al-Baghdadi’s elder sister, Rasmiya Awad, her husband, daughter-in-law and five children in the town of Azaz, in Aleppo province in northwestern Syria.
The region is administered by Turkey following a previous military campaign that was launched in 2016.
Erdogan said the suspects were being kept in detention centres in Turkey while the justice ministry decides how to handle their cases.
Al-Baghdadi blew himself up during an October 26 raid by US special forces on his heavily fortified safe-house in the Syrian province of Idlib. The raid was a major blow to his armed group, which has lost territory it held in Syria and Iraq in a series of military defeats.
Also Thursday, Erdogan said attacks continued in northeast Syria by Kurdish forces targeting either Turkish troops or their Syrian opposition allies, despite two separate truces brokered by Russia and the US last month, which halted Turkey’s military offensive.
At least 11 Syrian opposition fighters were killed in an attack on Thursday, Erdogan said, without specifying where or how it occurred.
The Turkish leader said Wednesday a total of 144 Syrian opposition fighters and 10 Turkish soldiers were killed during Turkey’s military operation into northeast Syria, which began on October 9.