Four members of staff from contractor Veolia are carrying out the work in Market Place, Bell Street, Duke Street and Hart Street.
The operation, which began on Monday and is expected to continue until the middle of next week, is costing the town council £5,500.
It involves sweeping rubbish and loose grit from the streets with a leaf blower, a street cleaning vehicle and hand tools before a handheld steamer is used to remove chewing gum and other stains.
The device has brushes and uses a cleaning chemical which Veolia says will not damage the York stone slabs.
Finally, the pavements are blasted with a high-pressure jet washer.
The council commissioned the clean-up as South Oxfordshire District Council no longer funds deep-cleaning. Henley Mayor Stefan Gawrysiak said: ?We want Henley to be not only the most beautiful town in Oxfordshire but the cleanest as well.
?We intend to do this next year and pay for it as a service to the residents of Henley.?
Cllr Gawrysiak has launched a campaign encouraging Henley?s shopkeepers to sweep the pavements outside their premises.
More than 60 businesses have signed up in support. He is also urging shoppers to put their rubbish in bins.
The Mayor said: ?We have two problems at the moment ? cigarette butts and chewing gum.
?Our message is very simple ? please don?t leave it on the street with your saliva all over it. It?s filthy, it?s messy and it?s horrible.?