The gay marriage ban triumphed at the polls in a 53 to 47 percent result.
The march started at about 5:30 p.m. on Friday. Helicopter images showed several thousand people moving up Market Street toward the Castro.
At its peak the crowd, which is estimated to be 5,000 people, filled Market Street and stretched from the Castro to the Civic Center.
The crowd wound through the Castro and into Dolores Park for a brief rally.
From there several smaller groups marched back to City Hall. Police say several people were arrested for public intoxication but there were no reports of violence.
The organizers of the march have said they place partial blame for the success of the measure on the Mormon church, which spent no official church money, but encouraged its members to fight against gay marriage openly on a regular basis.
March organizers said that participants were not affiliated with any agency, pro-human rights or otherwise. They said that a group of concerned citizens had organized the protest.
Organizers said they had informed the San Francisco Police Department that the march would take place.
Organizers said they had been posting and passing out flyers around the city. Hundreds of people said they were interested in participating.
Supervisor Bevan Dufty said he had coordinated with police, fire and MUNI to make sure the event was a safe, controlled one.
A similar protest is planned for Saturday night in Los Angeles.