Quantum dots (QDs) are nanometer-sized luminescent semiconductor nanocrystals. Their unique optical properties, such as high brightness, long-term stability, simultaneous detection of multiple signals and tunable emission spectra, make them appealing as potential diagnostic and therapeutic systems in oncology. Preparing the functional QDs by modifying bio-molecules such as antibody will have potential value for cancer diagnosis and treatment. This paper summarized the recent progress of promising application of QDs in cancer diagnosis and therapy, from identifying molecular targets, to drug delivery and therapy; from limitations of toxicity issues related to QDs in living organisms to multifunctional design and development. Finally, the promising applications of QDs are also discussed.