Composites nanomaterials are widely studied because of their important applications and unique structure that can be modified and controlled by different methods. In this work, three types of ZnO-CdS composites have been synthesized and applied as photocatalysts for the degradation of Rhodamine B dye in aqueous solutions. The optical and morphological properties of the prepared composites were characterized by different techniques. X-ray diffraction patterns used to identify the phase and to calculate the crystallites size of composites. The morphology and particle size of the composites were analyzed by transmission electron microscopy (TEM). Energy Dispersive X-Ray Analysis coupled with transmission electron microscopy used to measure the composites elemental content. Electronic and optical properties of the solid composites were analyzed by diffraction spectrophotometer. TEM results revealed that all ZnO-CdS composites have homogenous shape with (20-30 nm) particles size. XRD characterization indicates that the composites pattern belongs to wurtzite structure and the calculated crystallites size also in the nanometer. EDS results revealed that all ZnO-CdS composites contains only oxygen, Zinc, Cadmium and sulfur without impurities. UV-Vis measurements showed that the energy-gap of composites significantly decreased after heat treatment and all of prepared composites absorb visible light. The photocatalytic activity of prepared composites shows an excellent performance for RhB dye degradation in aqueous solutions.