The incident took place on Saturday morning, between 7.50am and 8.05am, between Tweedsmuir Road and Struan Road in Perth.
The woman was approached by a man, before being threatened with a knife and having her handbag and purse taken.
Police say the woman did not suffer serious injuries.
Described as between 20 and 30 years old, clean shaven and around 5ft 7in, the man was wearing a black jacket with its hood up and jeans.
Detective Sergeant Ryan Thompson said: "The victim was shaken but didn't suffer any serious injuries.
"If anyone remembers seeing anyone matching this description around the area at that time acting suspiciously, or has any relevant information, please contact us."
Witness have been urged to contact Police Scotland on 101, quoting the reference number 897 of October 26.