The robbery was reported at about 9:30 p.m. in the 2000 block of Mission Street between 16th and 17th streets.
The 27-year-old victim was walking along the street when a suspect approached and demanded his property. The suspect then took out a knife and slashed the victim in the side before taking his cellphone and cash and running away, police said.
The suspect, a man in his mid 60s, had not been found as of this morning.
The victim was taken to San Francisco General Hospital to be treated for his injuries, which are not considered to be life threatening, according to police.
Anyone with information about the robbery is asked to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.