It happened just before noon in Anderson Hall, a classroom building for the humanities.
Police say the 81-year-old professor was alone in an open office area when he was grabbed from behind.
The suspect punched the professor in the face and held him at knifepoint.
He then demanded the professor's wallet.
After taking the wallet, the suspect then punched the professor in the face again causing lacerations to the face and head, as well as swelling and bleeding to the professor's brain.
The suspect is described as black male, 35 to 40 years-of-age, with a mustache, close cropped beard. He was wearing a dark colored jacket, blue jeans and a lanyard around his neck.
The police and university are trying to figure out how the attacker got past security.
"To get up into the area where he was you need to be able to show an ID to a security guard that's working just outside the elevators," Temple University spokesman Ray Betzner said.
Temple students are occasionally victimized by crime off campus.
Most say they feel relatively secure on campus, but this incident has shaken them.
"Walking to and from campus is a huge concern for us and to hear it happening inside one of our buildings is even more alarming," senior Heather Jones said.
Stepped up security was extra visible around Anderson Hall after the incident.
The university says it works hard to provide a safe environment for faculty and students.
"We have a very safe campus at Temple University. We take a great deal of pride in the work that our police do in keeping our community safe. So when something like this does happen on those rare occasions, it's distressing," Betzner said.
Temple University police and Philadelphia police are both on the case hoping to identify a suspect as quickly as possible.
Anyone with information is asked to call Temple University Police at 215-204-1234.
