We report on the synthesis of CdSe/ZnX (X=S, Se) core/shell quantum dots from the CdO precursor through a convenient, one-pot approach. The defocusing stage (i.e., Ostwald Ripening) can be finely controlled to prepare nearly monodispersive core/shell quantum dots. The resulting particles have been characterized by their corresponding optical properties, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and powder XRD. This method is highly reproducible, and quantum efficiencies as high as 0.7 can be achieved. r 2004 Elsevier B.V. All rights reserved.