We identified a novel extracellular heme-binding protein and named it neuferricin. The recombinant mouse neuferricin produced in High Five cells was secreted efficiently into the culture medium. Mouse neuferricin mRNA was expressed mainly in the brain at the embryo stage and gradually increased during development. At postnatal stage, it was widely expressed in the brain, heart, adrenal gland, and kidney. Mouse neuferricin has 263 amino acids. It has a cytochrome b5-like heme/steroid-binding domain and appeared to bind hemin because neuferricin solution, but not a solution of neuferricinDeltaHBD (a mutant lacking the heme-binding domain), was tinged with brown and had an absorbance peak at 402 nm. In addition, the experiment with anti-neuferricin antibody using heme-affinity chromatography proved that the endogenous neuferricin detected in the culture medium of Neuro2a cells was associated with hemin. Inhibition of endogenous neuferricin by RNA interference excessively promoted cell survival and proliferation and suppressed neurite outgrowth during the induction of differentiation in Neuro2a cells. Addition of recombinant mouse neuferricin, but not neuferricinDeltaHBD, suppressed survival of Neuro2a cells and rescued from the effects of neuferricin RNAi. In primary cultured mouse neural precursor cells, recombinant mouse neuferricin exhibited the ability to promote neurogenesis. The identification of neuferricin, a novel extracellular heme-binding protein with cytochrome b5-like heme/steroid-binding domain and its neurogenic activity, provide new insights not only into brain development but also the function of heme-binding proteins as extracellular signal transmitters.