Display omitted ► Na 2S 2O 8 was activated by magnetite and ultrasound for the degradation of tetracycline. ► The presence of different types of radical scavengers would inhibit the degradation rate. ► The oxidation mechanism on the surface of the heterogeneous catalyst is scarce. The removal of tetracycline by magnetite (Fe 3O 4) activated peroxydisulfate (Na 2S 2O 8) in the presence of ultrasound irradiation has been performed in this study. The effects of Na 2S 2O 8 concentration, Fe 3O 4 addition, ultrasonic power, initial concentration and initial pH on the degradation of tetracycline were investigated. The results showed that tetracycline removal rate increased with the increase of Fe 3O 4 dosage, but decreased with the increase of initial pH and initial tetracycline concentration. With the optimum values of Na 2S 2O 8 concentration and ultrasound power, the highest degradation rate can be achieved. The scavenging effect was examined by using ethanol, tert-butyl alcohol and 1,4-benzoquinone to evaluate the roles of sulfate radicals, hydroxyl radicals and superoxide radicals. The results indicated that sulfate radicals and the hydroxyl radicals played important roles in the degradation of tetracycline by Fe 3O 4/Na 2S 2O 8/US process.