The purpose of this article is to analyze the terrorist activities of the Active Resistance Party of Finland («activists») and left-wing radical organizations in the Grand Duchy of Finland in 1903–1907. The article used such methods of scientific research as descriptive, historical, retrospective and comparative method. The article examines in detail the terrorist activities of the militants of the Active Resistance Party of Finland against the highest officials of state bodies of the Grand Duchy of Finland, namely, the plot describes the assassination attempt on Governor-Generals N.I. Bobrikov and I.M. Obolensky, on the governor of the Tavastgus province A.A. Papkov, on other high-ranking officials of the principality, and also tells about the murder of the prosecutor of the Finnish Senate E. Soisalon-Soininen (Johnsson) and the reaction to this murder of the Finnish society. In addition to the terrorist activities of the militants of the radical bourgeois Active Resistance Party of Finland, terror, as a method of combating the existing government, in the period considered in the article, was also carried out by left-wing radical organizations, which at the stage of their formation had the closest connection with the Active Resistance Party of Finland. The article analyzes the terrorist acts committed by such radical left organizations as «workers' activists», the Force of the Karelian people, «Bloody Dogs», as well as anarchists, including an unsuccessful attempt to assassinate Nicholas II by militants from the «Bloody Dogs» organization, during while the emperor was hunting in Björkö. The article provides information about the close military and revolutionary cooperation of the Active Resistance Party of Finland and radical left organizations with the Russian Socialist-Revolutionary Party, including in the preparation (making of bombs) and carrying out terrorist acts. The theoretical significance of the work lies in the analysis and definition of the place and role of terror as a political practice and method of struggle of various political forces of the Grand Duchy of Finland in 1903-1907, starting with the bourgeois-separatist Active Resistance Party of Finland and ending with small anarchist groups. The terror of the Finnish radicals, despite their declared politically "noble" goals of the struggle for the independence of Finland and the struggle for the liberation of labor from the yoke of capital, did not find mass support from the Finnish society, moreover, caused rejection in it, which became one of the reasons for the political collapse Active resistance parties in Finland and the collapse of left-wing organizations that relied on terror as a means to achieve their goals.