The victim got on a bus at the Tollgate bus stop on Borstal Hill at 12.10pm on Saturday 14 August 2021 and sat on the top floor.
A few minutes into the journey, he is said to have been punched a number of times to the face and body before he was told to hand over a quantity of money, which he did.
After the robbery, the victim remained in his seat until the bus arrived in Canterbury.
The suspects were described as a boys aged 16 or 17. One is described as being slim and was wearing a dark tracksuit with white stripes down the edges. The second is described as having a large build and was wearing a black hooded jumper and blue jeans.
Detectives would like to speak to anyone who was on the bus and saw the incident, or anyone with information regarding the robbery.
Witnesses should call Kent Police on 01843 222289 quoting 46/149358/21.
You can also contact Crimestoppers in Kent anonymously by calling 0800 555111 or by filling in the online report form at Crimestoppers-uk.org.