Semiconductor nanocrystals have been highlighted for the numerous applications in biological system. Major production routes to semiconductor nanoparticles are chemical synthesis involving harsh condition such as toxic organic solvent and high temperature. As an alternative, benign biosynthetic methods using biological molecules or live cells have been explored. Our strategy for making CdS nanocrystals is to construct a metabolically engineered E. coli to synthesize the cysteine-rich peptide, phytochelatin (PC), derived from plants and yeasts. Expression of PC, a stabilizing agent, with the supplement of CdCl2 resulted in PC-cadmium complex. Subsequent incubation with Na2S completed the formation of peptide-capped CdS nanocrystals. We demonstrated that cells producing PCs were able to synthesize CdS nanocrystals when exposed to both cadmium and sulfide. Detailed investigations on the properties of these CdS nanocrystals will be reported.