The Sunday Mirror said the Duchess of Cambridge had them changed from studs to drop baubles.
Kate wore the earrings, which match her engagement ring, on her first official visit with William to Canada and the United States this month. The ring had been presented to Diana by William's father, Prince Charles, more than three decades ago.
Kate wore the earrings for the first time when she and her husband attended Wimbledon in June.
"Now they're married, William wanted her to have some of his mother's favorite pieces," a courtier told the Mirror.
Prince William and Kate married in April.