Iron oxide nanoparticles, with diameters around 12nm, were synthesized by coprecipitation method. The magnetic properties indicate a superparamagnetic behavior with a coercive field of 9.7Oe and a blocking temperature of 118K. Both aqueous and solid magnetoliposomes containing magnetite nanoparticles have sizes below 150nm, suitable for biomedical applications. Interaction between both types of magnetoliposomes and models of biological membranes was proven. A new antitumor compound, a diarylurea derivative of thienopyridine, active against breast cancer, was incorporated in both aqueous and solid magnetoliposomes, being mainly located in the lipid membrane. A promising application of these magnetoliposomes in oncology is anticipated, allowing a combined therapeutic approach, using both chemotherapy and magnetic hyperthermia.