Prussian blue (PB), a kind of ferrous ferricyanide composed of Fe2+ and Fe3+, has been approved by Food and Drug Administration (FDA, USA) as an oral drug for the treatment of thallium and cesium poisoning. The biosafety of PB has been proved by long-term clinical trials. In recent years, PB nano-materials have attracted intensive research interests for medical application, especially for tumor imaging and treatment of cancer. Compared to other nano-materials, PB has potential advantage in medical application due to the high biosafety. This paper reviews the new advances in the functions of cancer diagnosis and therapy of PB nano-materials.