It was caught in gunfire while transporting a patient along Snyder Avenue, near 15th Street and Passyunk Avenue, just after 9 p.m.
The medic unit then dropped off a patient at Jefferson Hospital in Center City.
That is when medics notified police.
The bullet struck the passenger side mirror.
Police say none of the patients or employees were hurt.
Investigators are trying to figure out who fired the shot.