Abstract: Based on fluorescence resonance energy transfer(FRET)principle and the reductive environment in the cytoplasm, this study attempted to characterize the stability of the carrier in cells. A new probe conjugation with FRET and reduction responsibility simultaneously, (3-COOH-7-OH-coumarin)-(sulfur-sulfur)-(fluorescein isothiocyanate)(CHC-SS-FITC), was first synthesized. With liposome being used as model carrier, (CHC-SS-FITC)-liposome was prepared and the FRET effect and reduction responsibility of CHC-SS-FITC were assessed. The stability of drug-loading liposome in macrophages was investigated by laser scan confocal microscopy. Results showed that the reduction response FRET probes(CHC-SS-FITC)could be used to characterize the stability of nano-carrier in cytoplasm, due to the high sensitivity and strong counter-interference of the carrier.