We report on the preparation and on the photophysical and structural characterization of alloyed CdSe(S) nanocrystals, which are covered by a ZnO shell. CdSe(S) QDs were prepared by reaction of CdCl2 with NaHSe in the presence of 3-mercaptopropionic acid (MPA) under hydrothermal conditions. The incorporation of sulfur arises from the surface-mediated MPA hydrolysis on the growing QD surface. Water-dispersible CdSe(S) QDs were successfully capped with a ZnO shell obtained by basic hydrolysis of Zn(OAc)2. The experimental results from transmission electron microscopy (TEM) imaging and powder X-ray diffractometry (XRD) analyses indicate that the core/shell CdSe(S)/ZnO QDs have a very small diameter (ca. 2.8 nm) and exhibit a face-centered cubic crystal structure. Our results show that core/shell CdSe(S)/ZnO QDs have a higher photostability than CdSe(S) cores. CdSe(S)/ZnO QDs have potential applications asfluorescent biological labels and were successfully used for imaging Schewanella oneidensis bacterial biofilms.