Dmitry Pugachyov, head of the Courage and Humanism movement based in Salsk in the Rostov Region, was found guilty of making insulting statements and serious accusations against Anatoly Kashin, head of the Salsk district, at a rally in September 2006.
"The court has qualified Pugachyov's remarks against the district head and administration officials as libel," press secretary Sergei Didenko said. "Pugachyov failed to produce any evidence substantiating his statements at the rally."
The rights activist accused Kashin and his aides of corruption and bias in trade disputes in favor of a criminal group from Daghestan, in Russia's North Caucasus.
Pugachyov said he would appeal the sentence, which he insisted had been prepared in advance without a proper investigation and trial.
"I will certainly appeal the ruling... No [defense] witnesses or evidence were taken into consideration," Pugachyov said, adding as leader of a public organization he had spoken at the rally on behalf of society.
Russian justice has been notorious for being applied selectively and often for political purposes. Although President Vladimir Putin has ordered measures to curb corruption in all spheres as his term nears an end in 2008, corruption continues to plague the judiciary and police.
Foreign rights organizations blame this on a recent crackdown on NGOs and the media and the lack of transparency in government agencies.