The development of a theranostic nanoplatform based on rotavirus structural protein VP4-coated Fe(3)O(4) nanoparticles (NPs) for dual modality magnetic resonance/fluorescence cellular imaging and drug delivery is reported. VP4 protein was obtained from Escherichia coli approach, and then chemically conjugated to Fe(3)O(4) NPs premodified with meso-2,3-dimercaptosuccinnic acid (DMSA) in the presence of 1-ethyl-3-(3-dimethyaminopropyl) carbodiimide (EDC). Next, the VP4-coated Fe(3)O(4) NPs were loaded with doxorubicin (DOX), a typical anticancer drug, via formation of amide bond through the EDC approach. Prussian blue staining analysis reveals that the VP4-coated Fe(3)O(4) NPs can be internalized efficiently by MA104 and HepG2 cells, thereby significantly improving cellular MRI sensitivity, compared with dextran- and BSA-coated Fe(3)O(4) NPs. In addition, DOX loaded on the VP4-coated Fe(3)O(4) NPs exhibits significant cytotoxicity to the cancer cells (HepG2). The current work provides a general approach toward the rational design and synthesis of a versatile theranostic nanoplatform based on functional protein-coated magnetic NPs with good biocompatibility, biodegradability, and capability of simultaneously performing multimodality imaging and therapy for optimal clinical outcomes.