Democratic Rep. David Wu is resigning amid claims from an 18-year-old woman that he sexually assaulted her.
The California woman told Wu's office that she had an unwanted sexual encounter with the Oregon lawmaker.
Fellow party members called for a House ethics investigation within days of the allegations.
Wu, 56, said in a statement Tuesday that he intends to fight the "very serious allegations."
"The well-being of my children must come before anything else," he said. "With great sadness, I therefore intend to resign effective upon the resolution of the debt-ceiling crisis."
"This is the right decision for my family, the institution of the House, and my colleagues," he said.
Wu's hometown newspaper The Oregonian first reported the allegations. The paper said Wu told fellow aides the sexual encounter was consensual.
Wu has served seven terms in the House of Representatives.
In 2004, he won re-election despite acknowledging a decades-old college incident in which he tried to force a former girlfriend to have sex.
Wu, who separated from his wife more than a year ago, was first elected to Congress in 1998 as the first Chinese-American to serve in the House.