Microsoft has agreed to invest about US$100 million ($152 million) in Uber Technologies at a valuation of around US$50 billion, a source says.
The deal was finalised last week, the source said.
Uber, which was previously valued at US$40 billion when it raised financing earlier this year, is benefiting from investors who view its car-booking technology as the future of transport.
The San Francisco-based company, led by chief executive Travis Kalanick, is using the cash to expand operations to cities around the world.
"We filed to authorise this new funding more than two months ago," said Kristin Carvell, a spokeswoman for Uber. "The filing is available to the public. We aren't commenting on additional speculation."