Abstract: To improve the degradation rates towards methylene blue (MB), a composite catalyst Fe3O4@ZIF-9 was prepared by an ultrasonic assisted solvothermal method. When the molar ratio of Fe3O4 to cobalt salt was 1:1, spherical Fe3O4 particules were seen attached to the cube-shaped ZIF-9. It degraded 95.1 % MB within 30 mins, which was 5% higher than that of ZIF-8@TiO2 composites. Its degradation kinetic constant was 0.101 min-1, which was 8.78 times that of 10%TiO2@ZIF-8 composite. This may be attributed to the promotion of electron transfer by Fe and cobalt ions synergistically. The mechanism for activating peroxo-monosulfate is attributed to the synergistic effects of 1O2, ·OH and SO4-·. Its degradation rate remained almost the same after four cycles. Furthermore, it also possessed good ferromagnetism and recovery performance. This work may provide an insight to the techniques for organic dyes’ remediation.