Iron oxide nanoparticles with uniform size and narrow size distribution were synthesized by electrospraying of ferritin and subsequent heat treatment at 800 degrees, 850 degrees, and 900 degrees C. Solutions of ferritin in both water and water/iso-propanol mixture ( 50: 50) were electrosprayed in diverse gaseous environments. Narrow mobility size distributions with a mean mobility diameter of 4.5 nm and a geometric standard deviation < 1.2 were obtained at 800 degrees C. The process of aerosol formation involved the thermal oxidation of the ferritin organic shell. The utilization of a water/iso-propanol ( 50: 50) ferritin solution led to the establishment of a more stable electrospray, and, consequently, an increase in the total particle concentration was observed. Furthermore, carbon-coated magnetite (Fe3O4) particles were generated when CO was used as carrier gas.