European multimillionaires hold more than four times as much, with real estate accounting for 31 percent of their fortunes. Asian multimillionaires have 27 percent of their fortunes in real estate. Combined, Asians and Europeans hold more than a third of the residential real estate owned by multimillionaires worldwide.
In fact, North America ranked last among the world's regions when it comes to real estate holdings of the rich.
(Read more: Top states for millionaires per capita)
Paul Tostevin, of Savills' world research team, said the American rich have more of their wealth in financial investments and stocks than their global peers.
"I think in the U.S. there's more integration with the investment culture, and use of the stock market is more advanced," he said. "So real estate is a smaller share."