A 35-year-old woman jogging in Cannington was grabbed from behind and indecently assaulted on Monday.
Kensington Detectives ask for the public's help in their investigation into the assault.
A police spokesman said the woman was jogging south along the footpath on the southern side of Gibbs Street in Cannington around 7am when she was grabbed from behind.
The man held her in a bear hug and indecently assaulted her before he exposed himself and committed an indecent act.
The woman screamed and the man fled north along Gibbs Street.
The offender is described as being about 20 to 25 years of age, dark skinned with a medium build, approximately 180cm tall, clean shaven and short dark hair.
He was only wearing light coloured track pants at the time.
Anyone who may have seen the incident or has any information is asked to call Crime Stoppers on 1800 333 000.
Police would like to remind members of the public to be mindful of their surroundings at all times and safety tips can be found on the police website under Your Safety at www.police.wa.gov.au.