Transport for London (TfL) says the ride-booking app was not "fit and proper to hold a private hire operator licence".
It has 21 days to appeal the decision and can continue to operate until the end of any appeal process, TfL said.
"Private hire operators must meet rigorous regulations, and demonstrate to TfL that they do so, in order to operate", TfL said in a statement.
Also known as Uber Technologies Inc., it is an American technology company headquartered in San Francisco, California, United States, operating in 633 cities worldwide.
The Sun newspaper reported previous year that 32 sexual assault claims were made against Uber drivers in 2015/16, more than a fifth of all claims against taxi drivers filed to British police forces.
Uber said it plans to appeal and accused London's regulator of caving in to special interests "who want to restrict consumer choice".
Specifically, it cited Uber's approach to reporting serious criminal offences, background checks on drivers as well as software called Greyball that could be used to block regulators from gaining full access to the app.
But that didn't stop him from praising the company or tweaking drivers.
"Uber deserved to lose its licence", he wrote in an op-ed for the Guardian on Friday, adding that "all companies in London must play by the rules and adhere to the high standards we expect".
London's traditional "black cab" drivers have long campaigned against the service, and welcomed Friday's decision.
Business group London First said TfL's ruling "will be seen as a Luddite decision by millions of Londoners and worldwide visitors who use Uber", and would damage London's reputation as a global tech hub.
Uber drivers are categorised as self-employed which means Uber has little responsibility for them, or ensuring that they receive a fair wage.
Despite the accusation of failing to take passenger safety as seriously as it should, Uber denied it posed a safety threat to riders and said it had always followed the rules.
The Uber service has become the darling of most Londoners, but in a city filled with well-known black cabs and minicab firms, there are plenty of alternatives out there. Uber asked its customers to "defend the livelihoods of 40,000 drivers - and the consumer choice of millions of Londoners".
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