Size-selective CdS nanoparticles were synthesized on polyethylene (PE) films with surface-grafted poly(acrylic acid) (PAAc) chains by the stepwise immersion of the films into aqueous solutions of cadmium acetate and sodium sulfide. By varying the surface density of the PAAc chains, the soaking time, and the number of cycles, it was possible to control the degree of coverage of the film and the size of the CdS nanoparticles.