In the last decade, magnetic nanoparticles (MNPs), especially superparamagnetic iron oxide nanoparticles (SPIONs), have immensely promoted the advancement of diagnostics and theranostics in the biomedical field. The unique properties of the SPIONs-core and the functional gold (Au)-shell together (SPIONS/Au core/shell or CS) have a wide range of biomedical applications including, but not limited to, magnetic resonance imaging (MRI), dual modality MRI/computed tomography (CT), photo-induced and magnetic fluid hyperthermia (MFH), drug delivery, biosensors, and bio-separation. Researchers have made much effort to develop synthesis strategies for size control and surface modifications to achieve the desired properties of these CSs for applications in in vitro and in vivo studies. This review highlights recent developments in the synthesis and biomedical applications of SPIONs/Au CSs, including γ-FeO/Au (maghemite), FeO/Au (magnetite), and MFeO/Au (M = divalent metal ions) in the past seven years. More importantly, current trends of SPIONs/Au in relation to the biochemical industry are surveyed. Finally, we outline the developmental needs of SPIONs/Au from the perspective of material synthesis and their novel applications in disease diagnosis and treatment in the near future.