The incident took place at about 5.30am in The Gullet when the victim was pushed over by an Asian man in a black hooded top before being sexually assaulted.
The attacker, who ran away, is described as being in his 20s and has a moustache.
No arrests have been made.
Call 101 or Crimestoppers anonymously on 0800 555111.
Top Ten Articles
Police officers can be seen at Ten Pin Bowling in Maidenhead tonight following an incident earlier today.