She told about 60 residents Saturday at her New Hampshire nursing home that, "We are lucky to have him," The Boston Globe reported Sunday.
"I hope you'll vote for this man, who only comes once or twice in 100 years," said Kennedy, who has publicly compared Obama to her late husband.
She reminded attendees that the Kennedy family routinely spends Christmas and Easter skiing at New Hampshire's Waterville Valley.
"So we love New Hampshire, and we hope you love Obama," Kennedy said.
Sen. Edward M. Kennedy, D-Mass., and Caroline Kennedy, the daughter of assassinated President John F. Kennedy, also have publicly endorsed Obama.