The incident happened at 9:00 p.m. at the Citgo gas station located on the unit block of Levitt Parkway.
Police say the 67-year-old victim was out by the pumps when a man attacked him with a baseball bat, robbed him of an undetermined amount of money and fled on foot.
The attendant, who was struck repeatedly in the head and arms, was taken to Cooper University Hospital in serious condition.
Willingboro police are looking for a black male, approximately 5'11" tall, with a thin build and medium to dark complexion.
Police say he was wearing a hooded sweatshirt and dark pants and was last seen running toward the back yards of homes on Shawmont Avenue in Willingboro.
Anyone with information on the robbery or the suspect is asked to contact the Willingboro Police Department at 609-877-3001 or call the Citizen Tip Line at 609-877-6958.