Iron oxide nanoparticles (IONPs) are a promising material for the remediation of trace elements which are a significant source of soil pollution. Thus, as part of improving phytoremediation processes, the addition of IONPs to soil was tested in this study. A long-term experiment was performed in pot to assess the potential of magnetite (Fe3O4) nanoparticles (NPsMagn) to modify lead (Pb) availability to sunflower (Helianthus annuus) and its behavior in a water-soil-plant system under repeated water-deficiency stress. Plants were grown either in control soil, Pb polluted soil (final added lead 375 mg kg-1), Pb polluted soil containing 1 % dry weight NPsMagn or Pb polluted soil containing 1 % dry weight micro-sized magnetite for 90 days. Pb polluted soil and Pb treated soil containing NPsMagn do not affect plant growth but NPsMagn allow reduced oxidative impact as a decrease in lipid peroxidation was observed in their presence. Magnetic susceptibility measurements and Fe content in sunflower plants and leachates suggest that NPsMagn penetrate the roots but are not dispersed in soil solution. In addition, Pb content increased by 102 % and 22 % respectively in leaves and stems of plants treated with NPsMagn. Based on Pb content in soil solutions, NPsMagn decrease Pb in leachate by 50 %. During water stress periods, NPsMagn significantly improve water retention in soil and relative water content in plants. As a result of this, NPsMagn improve Pb availability and accumulation in sunflower plants in TEs contaminated soils unfavorable to plant growth. This study also highlights favorable effects of NPsMagn on Pb stabilization into soil, reducing their loss in leachates and on plant tolerance during water stress periods.