Herein, we design a facile and green method to synthesize luminescent superparamagnetic nanocomposites with a CdSe/CdS-Fe₃O₄ structure under mild conditions. This approach was performed in the solution phase at ∼90 °C (Fe₃O₄) and 60 °C (CdSe/CdS). Fe₃O₄ nanoparticles, prepared via a simple coprecipitation process, were used as seeds. A new route was designed to induce CdSe/CdS nanoparticle growth around the seeds for preparing bifunctional nanocomposites of CdSe/CdS-Fe₃O₄. In this approach, tri-sodium citrate plays an essential role in guiding and maintaining the structure of the nanocomposites. The fluorescence spectrum and M–H loops indicate that the bifunctional nanocomposites were synthesized successfully. It is proved that these bifunctional nanocomposites could be guided with a magnetic force for in vitro delivery into a human cancer cell line by a fluorescence microscope. The superparamagnetism and the high M_s (61.78 emu g⁻¹) of the Fe₃O₄ nanoparticles suggest that these nanocomposites also can be used as a T₂ Magnetic Resonance Imaging (MRI) contrast agent. The MRI images indicate that these bifunctional nanocomposites have potential applications in diagnostics as T₂ MRI contrast agents.