Nanotechnology is considered as Modern scientific revolution which has a large scale of applications in many fields including the biomedical applications, nanoparticles like carbon nanotubes, and metals/metals oxides nanoparticles as titanium, zinc, iron, silver, gold are used in diagnosis and treatment, studies showed that a lot of these nanoparticles could affect our cells and organs badly due to its toxic effect, so it is important to raise our knowledge about this toxic effect, in this article we will discuss the reported toxic effect of iron/iron oxides nanoparticles as one of the most common used one in many medical applications.