Schwarzman said the moves were partly justified by expectations for further economic growth as interest rates remain low. But that's led to higher purchase prices of assets.
"Everything is up. You have to see something reasonably remarkable in terms of your ability to improve the operations of a company," he said.
General Atlantic CEO Bill Ford, appearing on CNBC shortly after Schwarzman, agreed that valuations are getting lofty. "The only way you can justify these valuations is company quality and company growth."
In 2019, General Atlantic invested $4.5 billion in 31 new companies. General Atlantic is a private equity firm with about $35 billion in assets under management.
Blackstone, with $554 billion in assets under management, was also on a tear last year. In late 2019, it acquired U.S. industrial warehouse properties from Singapore-based logistics provider GLP for $18.7 billion, acquired shares of TallGrass Energy for roughly $3 billion, and took over the real estate assets of the Bellagio casino from MGM Resorts International for $4.25 billion.
However, Schwarzman said, finding value in 2020 may be more difficult.
"I wouldn't say stepping back," he said. "This is like a hockey game where you used to have 35 shots on goal, of things you could buy. Now, it's like five."
"You have much fewer things that are worth your time to analyze, but that doesn't mean those things won't happen," he added. "But your opportunity set is significantly reduced."
Schwarzman, who led the now-disbanded Strategic and Policy Forum, which was a group of CEOs who advised President Donald Trump, also said the "phase one" trade agreement between the U.S. and China is an "important deal."
"When these two don't have it right, it's a big deal," Schwarzman said. "I think it's in China's interest as well as in the U.S.'s to do a phase two deal."