Due to the special magnetic performance and nano-size, superparamagnetic iron oxide nanoparticles (SPIOs) have been extensively investigated in cancer diagnosis and therapy, such as magnetic resonance imaging (MRI), drug delivery, magnetic hyperthermia treatment, and so on. The development of nanomedicine brings challenges and innovations to magnetic materials, multifunction and integration become a kind of trend for material designs. Recent studies show that cancer-targeted MRI and drug delivery, or MRI-guided drug delivery and magnetic hyperthermia treatment in vivo, external magnetic field guided MRI, drug delivery and magnetic hyperthermia treatment in vitro, had become the research hotpots. This account presents a review on the recent progresses of SPIOs' applications in cancer diagnosis and therapy.