The suspect went into the Sonoma Federal Credit Union at 1126 Montgomery Drive shortly before 5 p.m., displayed a handgun and demanded money, police said.
A bank employee surrendered an undisclosed amount of money and the suspect fled on foot. No one was injured during the robbery.
The suspect was described as a man in his early 20s with a thin build, wearing black clothing. His face was covered during the robbery.
Anyone with information regarding the case is asked to call Santa Rosa police violent crimes investigators at (707) 543-3590.
