Contamination of water resources with antibiotics is an emerging environmental issue. This research reports the prosperous preparation of magnetic graphene oxide-polydopamine (M-GO-PDA) nanocomposite for sonocatalytic degradation of sulfadiazine (SDZ) as a model antibiotic pollutant from the aqueous solution. The physicochemical characteristics of the synthesized catalysts were analyzed by identification analyses including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), and Diffuse reflectance spectroscopy (DRS). After the operational variables optimization, the highest sonocatalytic degradation of SDZ (93.1%) was obtained using 0.45 g/L catalyst, 0.16 mM SDZ, and an ultrasonic power of 300 W at pH 6.8 (natural) within 60 min. Based on the observed data and GC-MS analysis, a possible sonocatalytic mechanism for the sonochemical degradation of SDZ in the presence of M-GO-PDA was proposed. Chemical oxygen demand (COD) removal efficiency of 79.4% and the considerable increase in the concentrations of SO42-, NH4+, and NO3- ions proved the effective mineralization of SDZ within 180 min sonocatalysis.