A molecule that can permeate phospholipid bilayer membranes (cell or endosormal membranes) is a useful carrier (i.e. vector) for therapeutic drugs (especially polymeric drugs). We studied the translocation ability of the hydroxyapatite (HAp) nanoparticle poly-L-lysine (poly(Lys)) complex through negatively charged phospholipid bilayer membranes (liposomes) using several instruments. Confocal laser scanning microscopy (CLSM) confirmed that HAp-poly(Lys) complexes can translocate through phospholipid bilayer membranes and also indicated that some of the complexes were retained in the inner aqueous water layer region the liposomes after translocation.