Uniform ZnxCd1-xSe nanocrystals have been prepared at the artificially designed water - oil interface using Na2SeO3, Cd(NO3)(2), and Zn(NO3)(2) as precursors. The chemical composition and band gap of the ZnxCd1-xSe nanocrystals can be adjusted via different combinations of source material. The coating of a SiO2 shell could transform the hydrophobic particles into hydrophilic particles. An advantage of this method is that a water phase could be added to the oleic acid (OLEA) synthesis system, which could be extended to make the synthesis of various nanocrystals more simple and flexible.