The protesters held photographs of reporter Oleg Kashin and environmental activist Konstantin Fetisov, who were savagely beaten in separate attacks this month.
Mr Fetisov was among those trying to save the Khimki forest from being cleared for road construction work, while Mr Kashin reported on the controversy. Both remain in hospital with head injuries.
Mr Kashin also had his jaw smashed, a leg broken and his fingers mangled.
Yevgeniya Chirikova, who heads the Khimki campaign, told the crowd: "With our action today we want to say hands off civil activists, hands off journalists, hands off the people who honestly express their views."
The bludgeoning of Mr Kashin by two unknown men, which was caught on a security camera and shown on television, has led to public outrage and demands that the attackers be found and punished.