Nanoparticles of a ZnS-CuInS2-AgInS2 (Z-CAIS) solid solution were prepared successfully via the thermal decomposition of single precursors in a hot oleylamine solution, their band gap being controlled by varying the chemical composition of the precursors. The morphologies of the nanoparticles changed from spheres to rods with an increase in the ZnS content in the particles. The photoluminescence intensity of Z-CAIS was relatively large, while ZnS-CuInS2 and ZnS nanorods prepared under the same reaction conditions exhibited no photoluminescence.