Britain's financial regulator, the Financial Services Authority, or FSA, has fined Swiss bank $47.6m for failings that led to trader Kweku Adoboli to commit the country's biggest fraud.
Adoboli, 32, was jailed last week for seven years after gambling away $2.3bn of the lender's money.
"UBS's systems and controls were seriously defective," Tracey McDermott, director of enforcement and financial crime at FSA, said on Monday.
A jury in London last week found the Ghanaian-born banker guilty of two counts of fraud, though it cleared him of four charges of false accounting.
UBS said it was "pleased that the chapter has been concluded", saying it had fully co-operating with the regulators' investigations.
The FSA said there were serious weaknesses at the Swiss bank.
It said in a statement: "UBS failed to take reasonable care to organise and control its affairs responsibly and effectively, with adequate risk management systems, and failed to conduct its business from the London Branch with due skill, care and diligence."
UBS said it was retraining staff on the importance of risk management and had changed the way it evaluated and compensated employees in order to make itself a simpler organisation.