Kennedy, who refused to disclose her financial information during her bid to take over Hillary Clinton's U.S. Senate seat in 2008, filed documents with the U.S. Office of Government Ethics for the ambassador position, the Post reported Monday.
"She's very rich, probably worth between $250 million and $500 million," a source who reviewed the documents told the newspaper. "From the figures, it looks like she earns between $12 million and $30 million a year from her trust and from her investments."
Along with family trusts, Kennedy, the daughter of U.S. President John F. Kennedy, also has holdings in Phil Falcone's Harbinger Capital, Apollo, Go.
In a letter that accompanied her financial documents, Kennedy said, "I understand that a heightened prospect of a conflict of interest could exist as to companies that maintain a presence in Japan."
She said she would step down from roles with the Institute of Politics at Harvard, the Kennedy Library Foundation, the Kennedy Center for the Performing Arts and her husband's Edwin Schlossberg Foundation if she's confirmed as the U.S. ambassador to Japan.