A novel photocatalyst of feather keratin (FK)-decorated CdS was synthesized by a simple co-precipitation method. Scanning electron microscopy (SEM) showed that the particle sizes of FK/CdS nanocomposites were smaller than pure CdS. The coexistence of FK and CdS in the photocatalysts was further confirmed by Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results of photocatalytic experiments demonstrated that the FK/CdS composites exhibit significantly enhanced photocatalytic activity for the photocatalytic degradation of RhB compared with pure CdS under visible light irradiation. The enhanced photocatalytic activity of the FK/CdS composites can be attributed to the similar affinity between FK and RhB, which can effectively separate the photogenerated electron–hole pairs. This method not only improves the photocatalytic activity of CdS, but also reduces the environmental pollution of waste feathers. In addition, the possible degradation mechanism of RhB is proposed.