The robbery occurred around 6:30 p.m. last Thursday in the 33900 block of 10th Street, according to police.
Police said the suspect approached the victim, pointed a semi-automatic handgun at her and demanded her property.
The victim handed over her belongings and the suspect ran away, heading west on J Street, police said.
Police are releasing an artist's rendering of the suspect, who is described as a black man between 35 and 40 years old. He stands bout 6 feet tall with a very thin build. He was wearing a blue dress shirt, black tie, black pants and a black baseball cap at the time of the robbery, according to police.
Anyone with information about this case is asked to call Union City police Detective J. Martin at (510) 471-1365.