Quantum dots (QDs) have shown unique optical properties compared with traditional organic dyes. Now, more and more attention has been paid to them, especially in the fields of biological medicine and materials. Much work about QDs application in biology has been done by many researchers. In resent years, QDs have been widely used as biological probes. By observing the conjugation site between QDs and target molecules or tracking the movement of QDs in live cells, some information about transferring signals mechanism may be obtained, therefore, offering apparent evidence for controlling cell's growth and finding the factors in the deterioration of cancer. In the present paper, interactions among macro molecules are introduced with fluorescence resonance energy transfer (FRET), fluorescent labeling of biological macro molecules, labeling and imaging of cells and tissues, and imaging in vivo. Furthermore, some developments and problems in application are summarized. Thirty seven references are cited.