The suspect, who wore a baseball cap and sunglasses, presented a teller with a note demanding all the large bills.
The suspect is described as thin, 25-30 years old with a small amount of facial hair.
No weapon was shown and there were no injuries.
The suspect was last seen running toward the VFW building near the bank.
He was later seen by a witness running toward Elm Street.
If you have any information please call Braintree Police at (781) 794-8600.