The white supremacist rally on Saturday was met by counter protesters, Sacramento Fire Department spokesman Chris Harvey told AFP.
The fire department posted on Twitter that some of the patients had "critical trauma stab wounds." It was unclear to which group the wounded belonged.
According to The Sacramento Bee newspaper, the stabbing spree broke out between some 25 neo-Nazis who had permission to protest on the capitol's west steps and more than 150 anarchists and "anti-fascist" counterprotesters.
The Los Angeles Times reported that a white-supremacist, anti-immigration group called the Traditionalist Worker Party staged the event.
Protesters had mostly cleared the capitol lawn, with only small groups remaining as of mid-afternoon, Harvey said.