The sexual assault happened Sunday night at the woman's home in the 900 block of Valley Drive.
The woman told police that she had just arrived home at about 8:30 p.m. when the man barged in and raped her. He then fled through the front door.
MORE: Manhattan Beach police looking for suspect who raped woman in her home
Police said he entered through an unlocked door. Authorities are warning residents to double check the locks on doors and windows.
Anyone with information is asked to contact Manhattan Beach Detective Jennifer Leach at (310) 802-5125 or call the Manhattan Beach Police Department Tip Line at (310) 802-5171.