A microwave-assisted ball milling process was used for low temperature synthesis of MgFe2O4 nanoparticles with high saturation magnetization. Four comparitive experiments, including boiling water assisted ball milling, microwave irradiation, regular ball milling, and microwave/ball milling alternative treatment, were also conducted to investigate the coupling effect of microwave and mechanical forces in the microwave-assisted ball milling process, which played a key role in the successful synthesis of MgFe2O4 nanoparticles. The concentrations of center dot OH radicals in the reaction solutions of these experiments were measured and used as an indicator for the solution reactivity. It showed that the concentration of center dot OH in microwave-assisted ball milling was much higher than that in microwave irradiation and regular stirring ball milling processes, confirming that the coupling of microwave and ball milling significantly enhanced the chemical reaction.