Difunctional fluorescent CoFe2O4 magnetic nanoparticles were prepared through a facile method. After the absorption of dopamine, human serum albumin (HSA) was easily attached onto the surface of CoFe2O4 magnetic nanoparticles through a reversible non-covalent bond between HSA and -NH2 in dopamine. With the same type of interaction, the designed perylene diimide (PDI) based -NH2 rich fluorescent molecule (PDI-4NH2) was decorated on the HSA-modified CoFe2O4 nanoparticles. The produced fluorescent magnetic nanoparticles exhibited great biocompatibility and could successfully enter the cell. Therefore, we have developed a novel method to obtain fluorescent magnetic nanoparticles with potential biomedical applications.