Bisphosphonates (BPs) are presently the treatment of choice for severe bone diseases due to bone resorption, such as osteoporosis, Paget's disease and bone metastases. In particular, zoledronic acid (ZOL) is a bisphosphonate able to act at micromolar concentrations. A recent study has shown that the efficiency of ZOL can be dramatically enhanced if it is administered in the form of self-assembling PEGylated nanoparticles. However, despite the high potentiality of these formulations, knowledge on their structural properties is still incomplete. Here we propose to use SANS to assess the structure of ZOL composite nanoparticles (also containing lipids from initial PEGylated liposomes). By this means we intend to elicidate the size and internal composition for further engineering of these self-assembly aggregates with high pharmaceutical interest.