We have prepared CdSe/ZnX (X= S, Se) quantum dots from the CdO precursor through a convenient, one-pot approach to maintain simplicity and green chemistry.39 Various characterization experiments provide unambiguous evidence for the core/shell nanoparticles formation. The feasibility of synthesizing tunable-size core/shell quantum dots may be considered an advantage, although the growing mechanism seems relatively complicated, as it may simultaneous incorporate the growth of core and the shell passivation. Nevertheless, the synthetic scheme described here optimized and finely controlled the defocusing stage, so that high-quality core/shell CdSe/ZnX quantum dots can be prepared in a one-pot synthesis.