The present invention has an object of providing a method by which two kinds or more of molecules can be separated each other by using dielectrophoretic forces. The present invention comprises two methods. The first method is a method comprising forming a complex substance of a "specific molecule" containing in a sample, and a "substance capable of changing dielectrophoretic properties of the specific molecule", which binds to the "specific molecule" contained therein, and thereby separating the complex substance and the molecules other than the specific molecule in the sample from each other. The second method is a method comprising placing a solution in which two kinds or more of molecules are dissolved under a strong electric field strength, that is, under a nonuniform electric field having an electric field strength of 500 KV/m or higher, by using dielectrophoretic forces.