In order to improve the chemical stability of quantum dots in application for quantum dot sensitized solar cells, we prepared CdXZn1-XTe/CdS core/shell quantum dots with type-II structure by an aqueous phase process using 3-mercaptopropionic acid as a stabilizing agent. We investigated the composition of Zn and Cd in CdXZn1-XTe quantum dots by using X-ray photoelectron spectrometer. The X-ray diffraction patterns confirmed the cubic zinc blende structure of CdXZn1-XTe quantum dots. In addition, we investigated the optical absorption, fluorescence emission and emission decay of samples, indicating that the energy level of ternary quantum dots can be controlled by both size and composition. Therefore, quantum dots with type-II structure can be prepared easily, which is benefitial to the improvement of fluorescence lifetime. We find that there are two decay processes in the emission decay kinetics of CdXZn1-XTe and core/shell CdXZn1-XTe-CdS quantum dots. The average lifetime of the photoexcited carriers is 24.07 and 39.80 ns, respectively.