The extremely small size of quantum dots (QDs) empowers them with properties that can be very useful in cancer treatment by photodynamic therapy (PDT) and bioimaging. The present work is focused on the evaluation of the cytotoxicity of water-soluble ZnS@ZnSe QDs, synthesized in presence of two different thiols (thioglycolic acid, TGA, and 3-mercaptopropionic acid, MPA), in human-pancreatic cells (PANC-1). The toxicity of Zn-based QDs was dependent of the type of thiol. The cell viability percentage decreased from 77.7% ± 7.1% down to 46.7% ± 0.9 % using 200 ppm and 300 ppm, respectively, of QDs synthesized with MPA. The viability of PANC-1 in presence of QDs synthesized with TGA decrease from 49.5% ± 8.8% to 46.8% ± 7.8% using 200 and 300 ppm, respectively. Our results suggested the feasibility of using Zn-based QDs at doses lesser than 200 pm as non-toxic fluorophores and as a potential material in nanomedicine.