The article describes an easy-to-implement and print-ready composition for inkjet printing of magnetic structures, which can be used for security printing, coding and marking, magnetic device fabrication and creation of micro-antennas. The synthesized inks are based on a biocompatible stable magnetite hydrosol and consist of monodisperse magnetite nanoparticles. The ink composition was optimized in order to ensure stable printing; the optimal printing conditions were achieved using the theory of Ohnesorge and by optimization of a piezoelectric waveform. In addition, the influence of the substrate material on drop formation was studied. The magnetic properties of the printed samples were measured using magnetic force microscopy (MFM). Printed thin magnetite films showed good magnetic response, and therefore the ink can be used for printing of anti-counterfeiting magnetic patterns.