"It did not turn out the way that I had thought it would, based on what he had said," she said of the eight-year Iraq War during a town hall event on "Good Morning America."
"And I regret that. And I said that it was a mistake and, obviously, is something that I wish hadn't turned out the way it did."
Clinton has in the past given different answers for what she thinks is her greatest political regret.
Responding to a question earlier this year about her greatest political regret, she mentioned not overhauling the healthcare system earlier.
"I regret we didn't get healthcare [reform] back in 1993 or '94, because we'd really be much further down the road," she said, according to AOL.com
She also previously named the 2012 terrorist attacks in Benghazi, Libya.
“My biggest, you know, regret is what happened in Benghazi. It was a terrible tragedy, losing four Americans — two diplomats — and now it’s public, so I can say two CIA operatives,” Clinton said, according to Politico.