The crime happened inside the Immaculate Conception Church at 414 East 14th Street at 6:30 Friday morning.
Investigators said a 61-year-old woman was praying when the suspect grabbed her from behind the neck and forced her to the floor.
The robber removed a brown leather purse from her hand, and then ran off.
Police said he headed west on 14th Street, then south on 1st Avenue.
Surveillance cameras caught the suspect running away. (Video above)
Anyone with information in regards to this incident is asked to call Crime Stoppers at 1-800-577-TIPS (8477).