She was so traumatised by the attack in Paisley, Renfrewshire, on January 29, that she only reported it to police recently.
The attack took place between 4pm and 7pm in a lane between Lansbury Gardens and Larkin Gardens in the Shortroods area of the town.
The woman, who was wearing a fawn-coloured jacket and jeans, was walking with the man for a short time before he attacked her.
The attacker is white, aged 40-45, 5ft 8in and has a slim-to-medium build.
He has black receding hair which is longer at the back, has a scar on his left cheek, a pierced ear and wore a grey jumper, or hooded top, and jeans.