The pop singer is reportedly still recovering from the flu and a bout with laryngitis as well.
This will be the second show that Rihanna has cancelled due to illness. She also scrapper her scheduled appearance in Boston on Monday night.
Fans who bought tickets for the Baltimore and Boston concerts are encouraged to hold onto their tickets pending a rescheduling of the show.
Rihanna is expected to be able to make her Thursday gig in Philadelphia.