At about 6pm on Friday July 22, the woman is said to have been walking from Infirmary Road onto Fox Road in the Upperthorpe area when an unknown man has approached her.
The man is said to have tried to engage the woman in conversation before reportedly sexually assaulting her, police said.
The woman then left the area and made her way home before reporting the incident to police.
The man is described as Middle Eastern, in his late 30s or early 40s and of slim build with a gaunt face. He was thought to have been wearing a khaki coloured t-shirt and jeans.
Anyone with informatin is asked to call 101 quoting incident number 443, or Crimestoppers can be contacted anonymously on 0800 555111.