The incident happened around 12:15 p.m. Monday on a Barta bus traveling along the 1900 block of Perkiomen Avenue.
According to police, 23-year-old William Smith of Birdsboro, Pennsylvania allegedly followed an 85-year-old woman off the bus.
He reportedly knocked her to the ground and stole her purse.
The victim suffered head injuries and dislocated her shoulder in the attack.
Police say a surveillance image helped them nab the suspect.