Billionaire investor Howard Marks took aim at bitcoin Wednesday, doubting the cryptocurrency's future in remarks at the eighth annual CNBC and Institutional Investor Delivering Alpha conference in New York.

"It's not an investment ... it's a trade," Marks said. "In the long run, I think it will be shown not to have any substance."

He said those who are buying bitcoin are only doing so "because they think someone will buy it from them at a higher price."

"Not because they can specify its intrinsic benefits. Not because they can judge the intrinsic value. But only because they think it's going up," Marks said.