In this paper, a series of Mn-Mg ferrites with the formula MnxMg1-xFe2O4(x=0.2,0.5,0.8) have been successfully prepared by ultrasonic-assisted ball milling approach. The characterization of the samples has been done using room temperature X-ray diffraction (XRD),transmission electron microscopy (TEM), vibrating sample magnetometer (VSM). The XRD results reveal that the formation of single-phrase ferrite is fully completed after 60 h. The TEM micrograph confirms that the average size of nanoparticles is about 25 nm. The maximum saturation magnetization of 74.22 emu/g is obtained when x=0.5, which decreases with the further Mn doping. The fluorescence measurements and electroconductivity detections reflect the reaction speed and confirm the coupling effect of ultrasonic and ball milling.