Aggregation induced emission (AIE) molecules are a type of compounds that emit weak fluorescence in diluted solution but emit strong fluorescence in aggregated state. Traditional organic fluorescent molecules tend to emit strong fluorescence in diluted solutions, but their fluorescence will be quenched in aggregated state, which are also known as aggregation-caused quenching (ACQ) effect. The effect is due to the excimer formed due to the π-π stacking between two molecules. AIE effect is first introduced by Dr. Benzhong Tang from university of Hongkong University of science and technology and till now, AIE molecules have been used in lots of different fields such as OLED, OFET, pH sensing, photo dynamic therapy and bioimaging. Bioimaging and biolabeling of AIE molecules have attracted more and more attention due to their high fluorescent quantum yield in aggregated state, highly resistance to photo-bleaching and large stokes shift. Incorporation of AIE characteristic and nanoparticles has become one of the dominant classes of imaging probes using organic fluorescent molecules. Continuing exploration for AIE theragnostic application will advanced the development or cancer diagnosis and therapy.