The lack of a sworn oath does not remove the possibility of criminal penalties against Clinton if she lied to the FBI, though he said he had "no basis to conclude" that she was untruthful.
"Still a crime to lie to us," Comey told the House Oversight Committee.
FBI policy is not to record interviews as part of its investigations.
Yet the revelations will nonetheless raise questions among Republicans, who have been skeptical of the FBI's investigation and have demanded to see the transcript of the former secretary of State's interview in downtown Washington on Saturday.
"Well, that's a problem," Rep. John Mica (R-Fla.) told Comey when the FBI chief explained the terms of the interview.
"It's pretty clear ... that the American people would like to see what Hillary Clinton said to the FBI," Senate Majority Leader Mitch McConnell (R-Ky.) told reporters on Wednesday, a day before Comey's appearance before House lawmakers.
Under FBI policy — and to the dismay of civil libertarians and staunch transparency advocates — the bureau does not conduct electronic recordings of interviews.
"Under the current policy, agents may not electronically record confessions or interviews, openly or surreptitiously" except in rare circumstances, the bureau said in a 2006 memo.
The FBI did, however, complete a federal form summarizing the interview, known as an FD-302, Comey said.
Mica recommended that a copy of that summary be provided to the Oversight Committee.
Comey himself was not among the "five or six" agents who interviewed Clinton, he testified on Thursday. But he assured lawmakers that Clinton told the truth throughout the session.
"I don't think the agents assessed she was evasive," he added.
Reader Comments
The FBI is accountable to the Director of National intelligence, James Clapper. As we are learning, release of primary information to the public yields an amazing analysis of the situation, with many points of view, and suggestions for further inquiry. So what is James Clapper going to do... get facts to the public, or cover for Hillary, as might be suggested in Ed Snowed's remarks?
"When Edward Snowden was asked during his January 26, 2014 TV interview in Moscow what the decisive moment was or why he blew the whistle, he replied: "Sort of the breaking point was seeing the Director of National Intelligence, James Clapper, directly lie under oath to Congress. … Seeing that really meant for me there was no going back."[30] [Link]