At about 9:45 p.m., the man knocked on the door of a home in the 900 block of Santa Lucia Drive, police said.
When one of the women opened the door the man displayed a black handgun and forced his way inside the home, according to police.
The man locked the women inside a bedroom and stole jewelry and electronics from the residence, police said.
He also stole one of the women's car keys, which he used to access a vehicle at the home and drive away from the scene, according to police.
The women, a 53 year old and 84 year old, did not sustain any injuries during the robbery.
The suspect is described as a white man in his mid-30s standing about 5 feet 11 inches to 6 feet tall with an average build and dark bread. He was last seen wearing dark clothing and armed with a black handgun.
The stolen vehicle is described as a silver 2013 Volkswagen Passat with California license plate 6XYC377.
Anyone with information on this incident is asked to call the Pleasant Hill Police Department's Investigations Bureau at (925) 288-4630.