This paper presents a simple and effective strategy to construct a UV photodetector based on ZnS hollow-spheres by oil–water interfacial self-assembly of polystyrene (PS)/ZnS colloidal nanospheres followed by annealing treatment. In this approach, PS/ZnS colloidal nanospheres were prepared and then self-assembled into a closely packed PS/ZnS nanofilm at a “hexane–water” interface. By annealing this precursor nanofilm under an optimal condition, a ZnS hollow-sphere nanofilm with a densely packed network structure was obtained. The particle size and morphology of the PS/ZnS colloidal nanospheres and the as-transformed ZnS hollow-spheres were characterized by TEM, HRTEM and SEM. Finally, a UV photodetector was successfully constructed from the as-transformed ZnS hollow-sphere nanofilm.