Magnetic nanoparticles (MNPs) possess different structural, magnetic and dielectric properties compared to bulk magnetic particles and they have found potential applications in the biomedical field (due to their response to applied magnetic field) including MRI, targeted drug delivery, bio sensors, tissue engineering, cancer therapy, and diagnosis, biomaterial coating devices, hyperthermia, cell selection and separation, magnetorelaximetry, antibacterial agent, biomolecules extraction, immunoassay, lab-on-a-chip etc. The synthesis of MNPs can be done by various methods pertaining to the application one is interested in. In present chapter we discuss basic properties (surface and magnetic) of magnetic nano particles and their biomedical applications.