Abstract This work presents an efficient method of largely synthesizing octahedral magnetite nanoparticles. Without any surfactant, octahedral magnetite nanoparticles were successfully achieved by means of an oxidation–precipitation method with ferrous sulfate as starting material, which was pro rata oxidized to ferric salts by NaNO 3 after alkalinizing with NaOH. XRD, TEM, SEM, ICP and VSM techniques were used to characterize the sample obtained by the above method. Experimental results indicate that the average size of particles is about 60–80 nm with a narrow size distribution and nanoparticles prepared show themselves in regular octahedral figures. The sample synthesized by the above method is in good crystalline state with good magnetic properties.