Observers say her endorsement of the Democratic Illinois senator, which came as it was reported her uncle, Sen. Edward Kennedy, D-Mass., would do the same, could pit the Clinton and Kennedy political dynasties against each other.
"I've been deeply moved by the people who've told me they wished they could feel inspired and hopeful about America the way people did when my father was president," Kennedy said in an op-ed published in The New York Times Sunday.
She said that inspiration is "even more profound today. That is why I am supporting a presidential candidate in the Democratic primaries, Barack Obama."
In Saturday's South Carolina Democratic primary, Obama handily beat Sen. Hillary Clinton, D-N.Y., and former North Carolina Sen. John Edwards.
"Sometimes it takes a while to recognize that someone has a special ability to get us to believe in ourselves, to tie that belief to our highest ideals and imagine that together we can do great things," Kennedy wrote. "We have that kind of opportunity with Sen. Obama."