A mixture of bis- and tris(fluoroaryl)borane compounds expressed by General Formula (1) below is handled in the form of a slurry made with a hydrocarbon solvent: where each of R1, R2, R3, R4 and R5 independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group, or an alkoxy group provided that at least one of R1-R5 represents a fluorine atom, X represents a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and wherein n represents 2 for the bis(fluoroaryl)borane compounds and 3 for the tris(fluoroaryl)borane compounds. Then, a hydrocarbon solution of the (fluoroaryl)borane compounds having a concentration of the tris(fluoroaryl)borane compounds in a range between 1 wt % and 1 wt % is prepared by dissolving the slurry into a hydrocarbon solvent in a virtually air-tight vessel. Consequently, it has become possible to provide a method of handling the tris(fluoroaryl)borane compounds in an industrially and economically advantageous manner, and a method of preparing the hydrocarbon solution of the tris(fluoroaryl)borane compounds readily and quickly without lowering the purity.