A series of ZrO2/Dy2O3 solid solution nano-materials with tunable compositions were successfully synthesized by the molten salt-assisted method. Structural characterization results show the positions, intensity, and width of the X-ray diffraction peaks of products show a regular variation with increasing Dy3+ content which implies the gradually changes of crystal spacing and product size. In addition, all the products are single phase without the coexistence of zirconia and Dy2O3 further demonstrating the perfect formation of targeted solid solutions. Photocatalytic experiments reveal that Zr0.8Dy0.2O2- nano-crystals have pretty photocatalytic degradation activities on Rhodamine B and Methylene blue under visible light irradiations. Reaction mechanism indicates that the excellent photocatalytic activities of Zr0.8Dy0.2O2- nano-crystals result from the special defect structure, smaller size, and larger specific surface area. It follows that Zr0.8Dy0.2O2- nano-crystals are promising visible light-responsive photocatalysts with better prospect in environmental protection and dye wastewater treatment. Moreover, the present molten salt-assisted route might be generalized to synthesize other solid solution nano-crystals with more complicated structures.