Bifunctional magnetic-optical Fe 3 O 4 /ZnO nanocomposites with different molar ratio were successfully synthesized by a facile two-step strategy. Compared with the other methods, it was found to be mild, inexpensive, green, convenient and efficient. Fe 3 O 4 nanocrystal was used as seed for the deposit and growth of ZnO nanoparticle. A series of the characterizations manifested that the combination of Fe 3 O 4 with ZnO nanoparticles was successful. Photocatalytic activity studies confirmed that as-prepared nanocomposites had excellent photodegradating behavior to Methyl Orange (MO) compared to the pure ZnO nanoparticles. The results showed that the degradation percentage of MO was about 93.6% for 1h when the amount of catalyst was 0.51gL −1 and initial concentration of MO was 6×10 −5 molL −1 in the pH 7 solution. Moreover, the kinetics of photocatalytic degradation reaction could be expressed by the first-order reaction kinetic model. Furthermore, the Fe 3 O 4 /ZnO nanocomposites could be also served as convenient recyclable photocatalysts because of their magnetic properties.