CdSe quantum dots (QDs) and polyaniline (PAni) were mixed to prepare CdSe QDs/PAni complex. PAni can quench the fluorescence of CdSe QDs. Fluorescence intensity of CdSe QDs/PAni complex is related to the size of CdSe QDs and the concentration of PAni. UV-Vis absorption spectra, fluorescence spectra, time-resolved fluorescence spectroscopy were used to analys the quenching phenomenon. The mechanism of fluorescence quenching is dependent on two factors: on one hand, the Forster resonance energy transfer from CdSe to PAni; on the other hand, PAni can intercept the charge relaxation process of CdSe and lead to the interruption of radiative recombination.