Water-soluble quantum dots of ZnSe@ZnS were synthesized under microwave irradiation at different temperatures in presence of thioglycolic acid (TGA). X-ray diffraction analyses suggested the development of a ZnSe-ZnS structure and an average crystallite size of 4.1 ± 0.4 nm. High-resolution transmission electron microscopy evidenced the formation of spherical nanocrystals. UV-vis analyses of nanocrystals synthesized at 120°C clearly showed the exciton peak centered at 290 nm. The corresponding photoluminescence spectrum evidenced a sharp and intense emission peak (FWHM ~ 32 nm) centered at 380 nm; the emission peak was broadened (FWHM ~ 47 nm) when the synthesis temperature was increased up to 140 °C. The strong emission in the nanocrystals synthesized at 120°C was attributed to the suitable development of the ZnS shell onto the ZnSe core.