We report a study on anion exchange reaction of CdTe nanocrystals with S2- in aqueous solution under ambient condition. We found that the optical properties of CdTe nanocrystals can be well tuned by controlling the reaction conditions, in which the reaction temperature is crucially important. At low reaction temperature, the product nanocrystals showed blue-shifts in both absorption and PL spectra, while the photoluminescence quantum yield (PLQY) was significantly enhanced. When anion exchanges were carried out at higher reaction temperature, on the other hand, obvious red shifts in absorption and PL spectra accompanied by a fast increase followed by gradual decrease in PLOY were observed. On variation of S2- concentration, it was found that the overall kinetics of Te2- for S2- exchanges depends also on [S2-] when anion exchanges were performed at higher temperature. A possible mechanism for anion exchanges in CdTe NCs was proposed. (C) 2015 Elsevier Inc. All rights reserved.