Gold bars were among the 7,408 valuables left inside Dubai's taxis by passengers during the first half of the year.
Money, mobile phones, passports and jewellery accounted for many of the other items.
Dubai Taxi Corporation on Sunday said 70 per cent of the items were returned to their owners so far.
Yousef Al Ali, chief executive of the DTC, said the total cash amount returned from January to June this year by honest taxi drivers was Dh640,000, excluding the monetary equivalent of other valuable items.
The single biggest amount returned to a passenger was $45,000 (Dh165,000).
According to the DTC, a part of Dubai's Roads and Transport Authority (RTA), there are about 12,000 male and female taxi drivers. Mr Al Ali said that the DTC has an "exceptional recognition and rewards scheme for the honest drivers" but he urged taxi users to be more mindful of their possessions.
People can report lost lost items through the call centre at 800 9090 or email@example.com.
"DTC is making every effort to fast track the delivery of lost items to clients as it appreciates the importance of such items," said Mr Al Ali.
The majority of taxis in Dubai are also fitted with surveillance cameras.