In spite of great advances in conventional cancer diagnosis and treatment, the early recognition and characterization for various cancers remain a technological bottleneck. The combined characteristics of board absorption and narrow emission make quantum dots (QDs) desirable fluorescent labels for cancer imaging and other applications in the biomedical field. In the current study, to the best of our knowledge, we first evidenced the preferential accumulation of QDs in cytoplasm of breast cancer cells. QDs therefore reveal considerable potentials in both tumor imaging and therapeutic application.