Police received a 911 call reporting the shooting in the 15500 block of Harbor Way around 9:20 p.m., Lt. Jeff Tudor said.
Officers arriving on the scene found the victim - a 33-year-old Asian American man - lying on the sidewalk with a gunshot wound to the chest, Tudor said.
He was taken to a hospital where he died from his injuries a short time later.
Police said two suspects approached the Alameda man's mother-in-law as she unloaded items from her car with the intention of robbing her. The man came out of the house to help his mother-in-law and one of the suspects shot him, Tudor said.
The suspects fled the area in a dark colored sedan headed for Lewelling Boulevard.
Police said investigators are actively searching for the suspects but have made no arrests.
Anyone with information about this case is asked to call San Leandro police at (510) 577-3230 or the anonymous tip line at (510) 577-3278.
Police said the killing is San Leandro's first homicide this year.