The construction of ternary semiconductor nanostructures has attracted much attention in photocatalysis by virtue of their tunable elemental composition and band structure. Here, ternary semiconductor ZnxAg1-xS (0 ≤ x ≤ 1) composites were successfully prepared by a simple and low-cost hydrothermal method without using any surfactant. Combined analyses using XRD, N2 sorption, SEM, TEM and UV-vis DRS revealed that the ternary composite semiconductor materials exhibited well-developed crystalline frameworks, large surface areas of 15-70 m2 g-1, sizes of 10-30 nm, and outstanding UV light absorption properties. Data from XRD and TEM indicate that photocatalysis might contribute to the formation of the strong interfacial interaction between ZnS and Ag2S nanoparticles. The photocatalytic activities were investigated via the degradation of organophosphorus pesticides, including malathion (MLT), monocrotophos (MCP) and chlorpyrifos (CPS), using the ZnxAg1-xS composites under UV light irradiation. The toxicity of MLT, MCP, and CPS was reduced by photocatalysis and photolysis; however, photocatalysis had a greater impact. Superior photocatalytic performance was exhibited by the Zn0.5Ag0.5S catalyst owing to its large surface area and the presence of Ag0 with improved charge transfer in comparison with that of bare ZnS and Ag2S. Assays of stability and reusability indicated that the Zn0.5Ag0.5S composite retained more than 85% of its activity after five cycles of use. On the basis of the results, a possible photocatalytic mechanism of the prepared samples was proposed. This study indicates a potential application of the ternary semiconductor materials in the efficient UV light-driven photocatalytic degradation of other pollutants that may cause environmental pollution.