A composition for controlling plant diseases, containing a pyridazine compound represented by Formula (I) and fipronil, exhibits an excellent control effect against plant diseases. The present invention provides a composition for controlling plant diseases, containing the pyridazine compound represented by Formula (I) and fipronil, and a method for controlling plant diseases, including a step of applying an effective amount of the pyridazine compound represented by Formula (I) and fipronil to a plant or soil for cultivating a plant. [In the formula, R1 represents a chlorine atom, a bromine atom, a cyano group, or a methyl group, and R2 represents a hydrogen atom or a fluorine atom.]