Magnetic-fluorescent nanocomposites have a tremendous potential in biomedicine realms as a revolutionary dual-modality probe tool for more accurate medical detection. However, complicated and inefficient postprocesses pose obstacles to obtaining high-quality magnetic-fluorescent nanocomposites. Thus, the fabrication of magnetic-fluorescent functional nanocomposites via a simple, effective, and ideal method remains a challenge and is still waiting to be tapped. The new synthesis approaches are becoming impending demands and probably enable us to address these abovementioned problems. In this contribution, we present a novel self-assembly synthesis route for the construction of magnetic-fluorescent bimodal imaging nanocomposites rather than adopting sophisticated postpreparative processes. The Fe3O4 and quatum dots (QDs) nanocomposites were cross-linked fleetly by cerium(III) ion driven coordination bonds in which the cerium(III) ions served as the cross-connecting node and the carboxylate groups acted as bridging ligands. The potential application for dual-modality imaging capability was validated on tumor-bearing mice. This ingenious strategy was extremely efficient and handy for the magnetic-fluorescent Fe3O4-QDs nanocomposite construction. Significantly, our cerium(III) ion driven self-assembly method probably has a wide applicability for nanoparticles and organic molecules containing carboxyl groups but extensive explorations are still necessary.