It happened at the intersection of Snyder Avenue and 12th Street at the Good and Plenty Mini Market just before 11:00 a.m. Thursday.
Police say the suspect got away with an unknown amount of cash and a cell phone.
The victim's husband, who identified himself as Mr. Chin, said his wife was injured when she fought with the robber.
The victim was rushed to Jefferson Hospital where she is listed in stable condition. Police are not releasing her name.
The suspect was last seen heading north on 12th Street. He was wearing black clothing, a black puffy jacket and may have had a slight beard.
Police spent the day scouring surveillance video from the store and around the neighborhood.
Investigators also say the knife used in the crime was found several blocks away. The black jacket the suspect was wearing has also been found.
Anyone with information is asked to contact Philadelphia Police at 215-686-TIPS (8477), text a tip to PPD TIP (773847) or through phillypolice.com.