In a letter to members of Congress, FBI director James Comey said the agency had finished its review and found nothing to change its position.
In July, he said Mrs Clinton had been careless but not criminal in handling sensitive material on her private email server while secretary of state.
The issue flared up again with the discovery of new “pertinent” emails.
They were reportedly found on the laptop of Anthony Weiner, the estranged husband of one of Mrs Clinton’s closest advisers.
“Based on our review, we have not changed our conclusions that we expressed in July with respect to Secretary Clinton,” said Comey in Sunday’s letter to Congress.
Comey’s original letter late last month to lawmakers, revealing that the bureau’s inquiry into Mrs Clinton’s emails had been revived, shook up the White House race and reinvigorated the campaign of Republican nominee Donald Trump.
The FBI director had said the agency would investigate if
the newly discovered messages contained classified information, reports the BBC