In this paper, a photochemical synthesis of ZnS-amorphous carbon nanotubes (ACNTs/ZnS) composites using ACNTs was reported, whose surface were modified with carboxylic groups as a support. The size and distribution of ZnS nanoparticles can be controlled by adjusting the initial amount of reactants and the reaction time. The ACNTs/ZnS nanocomposites were characterized by X-ray power diffraction, scanning electron microscopy and transmission electron microscopy. Studies showed that ACNTs/ZnS nanocomposites had high photocatalytic activity toward the photodegradation of dye molecule.