[en] CdS nanocrystals were prepared by a simple one-step aqueous synthesis method using thioglycolic acid (TGA) as the capping molecule. The effects of Cd precursor concentration and the TGA/Cd molar ratio on the photoluminescence properties of the CdS nanocrystals were investigated. It was found that both the remained free cadmium monomers and Cd-(SR)_x complexes played an important role in the nanocrystal nucleation growth and surface reconstruction. CdS nanocrystals with desired surface state could be obtained at high Cd precursor concentration and low TGA/Cd molar ratio