Richmond RCMP said that at about 11 p.m. PT, the woman walked south down No. 3 Road and then turned west onto Blundell Road.
That's where a man grabbed the woman from behind and sexually assaulted her.
Police believe it was a lone, random act.
"No similar incidents have been reported at this time," said Cpl. Stephanie Ashton.
The man, described as being between 5'7" and 5'9" and between 30 and 40 years old, has an oval face and short, cropped dark hair.
At the time of the assault, he was wearing black or dark-coloured knee-length shorts and a black or dark-coloured tank top.
Police are seeking information from anyone who recognizes the description of the suspect or who may have been near the scene of the assault.
"Any little thing that you might have seen, if you were out and about on No. 3 Road or near Blundell around 11 o'clock on Friday night, even if you think it's something really minor, do get in touch with us," Ashton said.
"You may not realize that it's something important," she said.
Google Maps: Brighouse Station to Blundell