A CdS/Cd₂SnO₄ composite was successfully synthesized via a one step solvothermal route synergistically assisted by L-cysteine and diethanolamine. The composite is composed of CdS quantum dots stuffed in hierarchical Cd₂SnO₄ microspheres with a diameter of around 2 μm, which are assembled from nanosheets with a thickness of 20–50 nm. The band gap of the composite is 2.46 eV, which is higher than pure phase CdS and Cd₂SnO₄, due to the quantum size effect from CdS QDs. One possible formation mechanism of the composite is presented; the initial precipitation of Sn(OH)₂ serves as a template, and the complexes of L-cysteine coordinated with metal ion provide structural direction for the hierarchical microspheres. The CdS/Cd₂SnO₄ composite showed superior adsorption ability and enhanced visible light photocatalytic activity in the degradation of RhB to CdS, Cd₂SnO₄, and Degussa P-25, due to its microstructure and the efficient charge separation at the interface of CdS and Cd₂SnO₄.