Abstract: Preparation of Sm-Fe mixed oxides powder by chemical co-precipitation method under ultrasound. The influences of microwave heating, ultrasonic power, ultrasonic duration, pH, dispersing agents, temperature, aging time on the particle size. And the morphology of precursor were compared and analyzed. The results showed that ultrasonic power 150 W, ultrasonic assisted time 15 min, pH value of 6, do not add a dispersing agent, aging time 1 h that can obtain the best precursor. The average particle size and dispersion of Sm-Fe mixed oxides powder that prepared under microwave is smaller and better.