Recent improvements based on heterojunction nanocomposites have opened new possibilities in photocatalysis. In this research, an ultrasound-assisted coprecipitation method was used to fabricate silver, zinc sulfide and reduced graphene oxide (Ag-ZnS/rGO) nanocomposite, and characterization results indicated that 3% Ag-ZnS spherical nanoparticles are successfully embedded in rGO matrix. The potential of the Ag-ZnS/rGO, as a visible light active photocatalyst, was assessed through optimizing degradation of Tetracycline (TC) by response surface methodology. It was found that the photocatalytic degradation of TC increased with an increase in the amount of nanocomposite and irradiation time, whereas it decreased with increasing the initial TC concentration. Under the optimal conditions (10 mg L of TC, 1.25 g L of Ag-ZnS/rGO, at pH = 7, and irradiation duration 110 min), more than 90% of the TC was degraded. The study of the mechanism of the photocatalytic process disclosed that the synergistic role of surface plasmon resonance (SPR) induced by Ag nanoparticles and p-type semiconductor feature of rGO leads to ZnS semiconductor stimulation in the visible light region. Eventually, a pseudo-first order kinetics model was developed based on the proposed mechanism. The obtained results highlight the role of Ag-ZnS/rGO nanophotocatalyst toward degradation of some antibiotics under visible light.