Moscow's Babushkinsky District Court has found opposition figure and anticorruption campaigner Aleksei Navalny guilty of slander.
Moscow City Duma Deputy Aleksei Lisovenko filed the lawsuit after Navalny allegedly posted a message on his Twitter account referring to Lisovenko as a "drug addict."
Judge Anna Nekryach ruled on April 22 that the comment was slander and ordered Navalny to pay a fine of 300,000 rubles ($8,350).
Navalny has been under house arrest since the end of February for taking part in an unsanctioned rally.
He is currently serving a five-year suspended sentence on a theft conviction, which he calls politically motivated.
Based on reports by ITAR-TASS and Interfax