Lipidic magnetic nanoparticles are a rapid and reliable magnet-guided nucleic acid delivery system, which we have named as “LipoMag” (Namiki et al., Nat. Nanotechnol 4:598–606, 2009). LipoMag is composed of a cationic lipid shell, an oleic acid binder, and an iron oxide nanocrystal core. Through the electrostatic force, positively charged LipoMag and negatively charged nucleic acid form complexes, termed “mag-lipoplex.” Under a magnetic field, LipoMag bearing nucleic acid can be controllably accumulated in target cells. Here we describe the procedure for the preparation of LipoMag which can be used for the transfection of nucleic acids, such as plasmid DNA and small interfering RNA.