Monolayer of octadecylamine（ODA） and salmon sperm DNA or salmon sperm DNA-Cd complex were studied on air-water interface by π-A isotherm. After being co-transferred onto substrates by Langmuir-Blodgett technique, atomic force microscope（AFM） measurements show the DNA molecules are packed into lines in the film, due to the interactions between the ODA and DNA molecules. By exposing the ODA and DNA-Cd complex LB film to H2S, needle-like CdS nanoparticles were formed along the DNA lines as characterized by transmission electron microscope（TEM）. Electron diffraction（ED） image indicates that the so prepared needle-like CdS is a new kind of nanostructured materials.
