The 23-year-old was walking on Crow Road in Glasgow when a man threatened her, took her into a wooded area and attacked her, Strathclyde Police said.
The man is described as Middle Eastern in appearance, about 5ft 8in, of slim build and in his mid-20s. He was wearing a white tracksuit jacket and spoke with a Glasgow accent.
Detective Inspector Fil Capaldi said: "A young woman has been left extremely traumatised and has been subjected to a sickening attack and it's absolutely imperative we find the man responsible.
"I am appealing to anyone who may have been in the area that morning, possible passing taxi drivers, people going home after a night out or local residents, who may have seen or heard something, please get in touch with us, your information is vital in helping us to trace the man responsible."
The attack happened at about 2.15am on Monday. The woman was walking near to Cross Park in the Partick area.