Abstract Inorganic nanomaterials that interface with biological systems have recently attracted widespread interests in cellular and biomedical applications. Semiconductor quantum dots (QDs) are among the most promising emerging fluorescent labels for cellular imaging. In this thesis, to study the way into cell、biocompatibility and photostability of QDs, we fluorescently labeled breast cancer cells ( MCF 7 ) using water-soluble CdSe/ZnS core-shell nanocrystals. Confocal microscopy images indicated that the cells remained stably labeled for several days and continued cell division. However, to establish whether QDs can specifically label organelles at a subcellular level, we used QDs modified with the nucleus localization signal ( NLS ) peptides to label the nuclei of the cells. The results showed that much labeling signals are specific for the nuclei and are brighter and considerably more photostable than comparable organic dyes. These results encourage the construction of more complex functional QDs for protein tracking in cell.