Determination of chondroitin sulfate in the biomedical field has an important value.The conventional methods for the assay of chondroitin sulfate are still unsatisfactory in sensitivity,selectivity or simplicity.This work aimed at developing a novel method for sensitive and selective determination of chondroitin sulfate by fluorimetry.We found that some kinds of cationic surfactants have the ability to quench the fluorescence of tetrasulfonated aluminum phthalocyanine (AlS4Pc),a strongly fluorescent compound which emits at red region,with high efficiency.But,the fluorescence of the above-mentioned fluorescence quenching system recovered significantly when chondroitin sulfate (CS) exits.Tetradecyl dimethyl benzyl ammonium chloride(TDBAC)which was screened from all of the candidates of cationic surfactants was chosen as the quencher because it shows the most efficient quenching effect.It was found that the fluorescence of AlS4Pc was extremely quenched by TDBAC because of the formation of association complex between AlS4Pc and TDBAC.Fluorescence of the association complex recovered dramatically after the addition of chondroitin sulfate (CS) due to the ability of chondroitin sulfate to shift the association equilibrium of the association,leading to the release of AlS4Pc,thus resulting in an increase in the fluorescence of the reaction system.Based on this phenomenon,a novel method with simplicity,accuracy and sensitivity was developed for quantitative determination of CS.Factors including the reaction time,influencing factors and the effect of coexisting substances were investigated and discussed.Under optimum conditions the linear range of the calibration curve was 0.20~10.0μg·mL-1.The detection limit for CS was 0.070　μg·mL-1.The method has been applied to the analysis of practical samples with satisfied results.This work expands the applications of AlS4Pc in biomedical area.