Oxytetracycline (OTC) is a typical antibiotic that poses a serious threat to the environment. However, traditional treatment methods suffer from low treatment efficiencies and potential secondary contamination. Therefore, there is a need to develop efficient, convenient, and environmentally friendly removal technology. In this paper, magnetic nano-Cu/Fe composites were successfully synthesized and used as the activator of peroxymonosulfate (PMS) to degrade OTC. The obtained catalysts with different ratios showed excellent degradation effects, especially the Cu/Fe-1 catalysts. The highest removal efficiency of OTC (93%) was achieved with 0.2 g L⁻¹ PMS and 0.1 g L⁻¹ catalyst in 60 min. The impacts of the catalyst and PMS dosages, initial temperature and pH, coexisting anions, microplastics, and real-life water samples were investigated. To explore the mechanism for OTC degradation, radical scavenging and electron spin resonance (EPR) experiments were carried out, and non-radical ¹O₂ was identified to be the main radical. TEM and XRD results show the presence of CuFe₂O₄ composites in Cu/Fe-1, which can promote the production of ¹O₂ and thus improve the OTC degradation efficiency. This work provides a new efficient, stable, low-cost, and environmentally friendly approach for the degradation of oxytetracycline.