It was the first time he was questioned since being detained last Wednesday. Chen is accused of money laundering and misusing a special fund during his eight years in office. His term ended in May.
Prosecutors did not brief the media about the interrogation.
Chen was in a good condition health-wise, said his defense lawyer Cheng Wen-lung.
Chen refused to eat while in detention and was sent to the hospital on Sunday night.
On the same day, prosecutors also questioned four other suspects, including Chen's former secretary and close friends of his wife Wu Shu-jen.
Chen's office treasurer, Chen Cheng-hui, was released Thursday after cooperating with prosecutors in the investigation, the first among ten detained suspects in this case.
Prosecutors said there remained little chance for her to collude with other suspects so continued detention wasn't necessary.
