A 4-aryl-4-substituted pyrazolidine-3,5-dione derivative represented by the formula (1) is useful as an effective component of a miticide, insecticide or herbicide
wherein R1 and R2 are each independently alkyl group having 1 to 4 carbon atoms, or R1 and R2, when taken together, represent saturated or unsaturated bivalent hydrocarbon group having 3 or 4 carbon atoms which may optionally be substituted with alkyl group having 1 to 4 carbon atoms, or halogen atom, X is alkyl group having 1 to 4 carbon atoms, haloalkyl group having 1 to 4 carbon atoms or halogen atom, Y is halogen atom or nitro group, and n is an integer of 0 to 3.