Abstract: Previous studies on the activity of bio-molecules in a cell were mostly performed on the basis of ensemble averaging. However, with the advent of new technology, especially optical and fluorescence techniques, it is now possible to visualize the dynamics and kinetics of a single bio-molecule in the living cell in real time. From the methodological aspect, many techniques are now available: fluorescent resonance energy transfer, atomic force microscopy, total internal reflection fluorescence, fluorescence correlation microscopy, and so forth. The investigation of single molecule behavior will probably open a new horizon in the future biological study. However, still many technical limitations existed, for example, the lack of small molecule fluorescent probes and new types of microscope with higher resolution beyond diffraction barrier, the difficulties in visualizing small fluorescent spot in the cell interior.