A facile and reproducible method has been demonstrated to prepare Au-CdS core-shell nanocrystals with controllable shell thickness. The study also demonstrated various photoinduced charge separation properties taking place in the core-shell nanocrystals during the synthesis process. It was observed that the binding of L-cysteine-Cd2+ complexes toward Au nanoparticles caused the growth of CdS shell on Au nanoparticles. It was also found during the study that the increasing thickness of CdS shell can cause a red-shift in the SPR position of Au. The growth of shell thickness also made a positive impact on the improvement of the overall refractive index on the medium surrounding of Au. The study concluded that this synthetic method can be used to prepare sulfide-semiconductor-coated Au nanocrystals like Au-ZnS.