A stretched single lambda DNA molecule labeled with TOTO-1 dye molecules was immobilized on a cover slip by casting a solution of DNA-lipid polyion complex containing TOTO-1 dye, and were loaded with an aqueous solution of histone. Fluorescence microscopy applied to the single DNA showed that (1) the TOTO-1 dye molecules intercalated in the stretched DNA molecule were vertically aligned almost completely with respect to the DNA axis, and (2) the stretched DNA was cleaved by interaction with histone molecules.