ZnO/C photocatalysts were successfully synthesized through the simple one-step calcination of zinc acetate dihydrate and glucose at 350 °C. The materials were characterized by XRD, TEM, FT-IR, and UV to ascertain their nanostructure, crystallographic phase, morphology, and photocatalytic properties. The ZnO/C composites displayed excellent photocatalytic activity for the degradation of methylene blue as compared with pristine ZnO. The best performance was achieved with the ZnO/C composite containing 1.5% carbon, in which the carbonaceous material assisted the adsorption of the water pollutant, effectively extended the absorption range to the visible light region, and improved the separation rates of photoelectrons and holes.