The first aqueous preparation of luminescent US QDs from a single precursor is reported. These water-soluble US quantum dots with tunable sizes between 25 and 40 Angstrom were produced from a readily prepared [(2,2'-bipyridine)Cd(SC{O}Ph)(2)] complex by simply refluxing in an aqueous solution. The as-prepared nanoparticles are fairly uniform in size without the need of size sorting, and exhibit a quantum confinement effect. The size of the nanoparticles is tunable by varying the capping agent-to-precursor molar ratio. The green- and yellow-emitting quantum dots obtained via this simple route are water soluble and have OH functionality that is suitable for further applications. The particle aging kinetics was investigated by monitoring the optical band edge absorption and was found to follow the Ostwald ripening mechanism. When the amount of capping agent used is 10 mmol, unprecedented dimerization of some QDs upon prolong reflux to form nanocrystals double the size is detected. Thus, a common red shift of the absorption band edge is not detected and the growth of larger QDs seems to arise from the coalescence of two QDs.