According to one report, SoftBank is offloading around $2bn (£1.44bn) worth of shares to help cover what it has lost by betting on Chinese ride-hailing firm Didi and other investments.
Didi’s shares have slumped since their US market debut less than a month ago.
That’s after a series of actions by Chinese authorities spooked investors.
By selling 45 million shares in Uber the SoftBank Vision Fund will cut its stake in the company by around a third.
The Japanese technology investment group has lost a total of around $4bn on its stake in Chinese ride-hailing firm Didi, according to CNBC.
However, Reuters news agency reported that SoftBank’s decision to cut its Uber stake was unrelated to the slump in Didi’s value and it just felt now was a good time to take some profits.
In 2018, SoftBank poured around $7.6bn into Uber and added another $333m to that investment the following year.
SoftBank is Didi’s largest shareholder, with a stake of more than 20%.
Uber also owns almost 13% of Didi after the US-based company sold its operations in China to its local rival five years ago.
Chinese technology companies traded in the US, Hong Kong, and mainland China have seen their market value fall sharply in recent months as Beijing tightens its grip on the industry.
Didi shares have fallen by almost 40% since they started trading on the New York Stock Exchange on 30 June.
Just two days after that US market debut China’s internet regulator ordered app stores to stop offering its Didi platform, saying it illegally collected users’ personal data.
Uber shares were down by as much as 5% in extended New York trading.
SoftBank did not immediately respond to a BBC request for comment.