Thanks to their magnetic properties, superparamagnetic iron oxide nanoparticles are considered as a good delivery vehicle after grafting a therapeutical drug on their surface. For additional “stealth” characteristics, PEGylation of surfaces is necessary. The presence of PEG chains divert nanoparticles from their preferred target, the liver macrophages and increased the particle time circulation. In this work, PEG chain is added to an anticancer drug Alendronate. This molecule is grafted on iron oxide nanoparticle surface in one step surface functionalization method. The in vitro cytotoxic efficiency of γ-Fe2O3- Alendronate-PEG nanocrystals is compared with that of free Alendronate, Alendronate-PEG and γ-Fe2O3- Alendronate nanocrystals.