In this work, the effect of four different precipitating agents on the structural and magnetic properties of synthesized ferromagnetic nanoparticles (FMNPs) by the co-precipitation method has been explored. In particular, different precipitating agents used in work include (I) NH3, (II) NH3 with alcohol, (III) NaOH, and (IV) aqueous NH3 solution. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (FESEM/EDS), zeta-potential, and vibrating sample magnetometer (VSM). From the XRD pattern and Debye-equation, it appears that the obtained nanoparticles were magnetite with an average crystallite size of 8–27.6 nm. The FTIR spectrum of NH3 in an alcohol solution indicates a perfect stretching of the Fe–O, O–H, C–H functional groups compared to other cases. Moreover, superparamagnetic behavior at room temperature was also noticed from VSM analysis. NH3 in an alcohol solution as a precipitating agent showed higher magnetic properties of FMNPs than the other cases. Conversely, the response time was found to be the longest for the same set. The procedure with NaOH in an aqueous solution was the cheapest with a shorter reaction time. Nevertheless, the particle surface and magnetic characteristics were lesser than the other cases of precipitating agents. © 2022 Elsevier B.V.