A monthly travelcard costs £135 ($174), according to a Deutsche Bank report - £33 ($43) more than Dublin, which was ranked second priciest city.
Auckland, where a ticket costs £95 ($123), came third, while New York City, at £91 ($118), came fourth, and Tokyo fifth at £86 ($111).
Transport for London (TfL) said the findings did "not show the true cost of transport in other countries".
The survey also found the cost of travel in the capital dropped since 2014, when commuters paid £165 ($213).
Source: Deutsche Bank
Its authors ranked London tenth most expensive for petrol, and the third for car hire.
Hong Kong had the priciest petrol, while Amsterdam was the most expensive for a daily car rental, the report said.
London's taxis fared slightly better, ranked 20th in a list of 47 cities, with Zurich topping the list for the most expensive fares.
For quality of life, London was ranked 33rd in the world, similar to other "mega cities" such as Tokyo, Paris and New York.
According to the report, these cities "rank very low" for quality of life, mostly due to "high living costs, crime, pollution and commuting time".
"This is highly subjective and one person's long commute may be another person's chance to catch up on Netflix," the report said.
"Megacity dwellers may also forsake short-term quality of life for aspirational reasons," the report added.
Wellington, in New Zealand, was ranked as the best city to live in in terms of quality of life, followed by Edinburgh, Vienna. Melbourne and Zurich.
In February, TfL revealed its fares income was down £90m last year.
TfL is currently planning to cut £16bn from its budget by 2020/21 as it  aims to become self sufficient with its operating costs.
The Mayor of London, Sadiq Khan, has frozen fares on buses and trams until 2020, but travelcard prices are set by train operating companies and so are not under full TfL control.
A TfL spokesman said: "London also has one of the most extensive set of travel concessions in the world with free or discounted travel for children, the over-60s, students and veterans."
Public transport in London is the world's most expensive, a report says.