The blood-brain barrier (BBB) restricts the delivery of many potentially important therapeutic agents for the treatment of brain disorders. An efficient strategy for brain targeted delivery is the utilization of the targeting ligand conjugated nanoparticles to trigger the receptor-mediated transcytosis. In this study, transferrin (Tf) was employed as a brain targeting ligand to functionalize the fluorescein-loaded magnetic nanoparticles (FMNs). The Tf conjugated FMNs (Tf-FMNs) were characterized by transmission electron microscopy, thermal gravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Using fluorescein as an optical probe, the potential of Tf-FMNs as brain targeting drug carriers was explored in vivo. It was demonstrated that Tf-FMNs were able to cross the intact BBB, diffuse into brain neurons, and distribute in the cytoplasm, dendrites, axons, and synapses of neurons. In contrast, magnetic nanoparticles without Tf conjugation cannot cross the BBB efficiently under the same conditions. Therefore, Tf-FMNs hold great potential in serving as an efficient multifunctional platform for the brain-targeted theranostics.