The woman was walking her dog in Whitstable, Kent, when she was grabbed in an alleyway by a man dressed in black and wearing a hooded top.
She fought off her attacker by punching him in the mouth. Kent Police say they are looking for a suspect with an injured face.
Detective Chief Inspector Paul Fotheringham, of Kent Police, said: "It appears the suspect has picked on the wrong person."
The attack took place early today in an alleyway between Bellevue Road and Invicta Road, the BBC reported.