This paper presents experimental results on weakly magnetic field-assisted synthesis of magnetite (Fe 3 O 4 ) nano-particles in an oxidative co-precipitation method, in comparison to the case without magnetic induction. The XRD results show that a weakly magnetic induction below 220Gs could accelerate the phase transformation from goethite (α-FeOOH) to magnetite (Fe 3 O 4 ), and affect the crystal structure, the particle size/morphology and magnetic response of the magnetite nano-particles synthesized. In addition, a higher concentration of the FeCl 2 solution in the synthesis reaction led to finer particles, both with and without magnetic induction.