The FBI says the female robber held up a Bank of America on Paramount Boulevard on Monday afternoon.
Since July 12, the suspect has hit seven banks in Southern California, including two in Moreno Valley and heists in Wildomar, Santa Fe Springs, Whittier and Buena Park.
The FBI says during the robberies, the suspect uses written and verbal demands, and indicates that a second person is waiting for her outside the bank. No accomplice has ever been seen.
The suspect was given the nickname "Plain Jane Bandit" after a witness in an earlier incident described her as a plain Jane.
Officials with U.S. Bank are offering a reward of up to $10,000 in exchange for information leading to the arrest and conviction of the suspect.
Authorities say she may be driving a silver, four-door car with a sunroof. She's believed to be 35 to 40 years old, 5 foot 3 to 5 foot 5 and weighs up to 170 pounds.
Anyone with information is urged to call the FBI at (310) 477-6565.
The Associated Press contributed to this report.