It happened just after 3 p.m. on Monday in the 5700 block of Chew Avenue.
A 75-year-old woman was walking westbound on Chelten Avenue, crossing Chew Ave. in the crosswalk, when she was hit by the bus. The bus was traveling eastbound on Chelten Ave, police said.
The pedestrian was taken to Albert Einstein Medical Center, where she was placed in critical condition.
No one was injured on the school bus, police said.
The investigation is active and ongoing with the Crash Investigation Division.