Abstract: Four Brønsted acidic ionic liquids (ILs) were synthesized using 1-methylimidazole, 1,3-propane sultone, sulfuric acid, phosphoric acid, tetrafluoroboric acid and p-toluene sulfonic acid as raw materials. Their structures were characterized and the acidity H0 was measured. These ionic liquids were applied to the synthesis of bisphenolfluorene. When the H0 was less than or equal to 1.94, the ionic liquid had cata-lytic effect, when that was less than or equal to 1.69, the ionic liquid had applicable value. A method for the determination of bisphenolfluorene by liquid chromatography was developed. The reaction products were separated and the structures of the three products were determined by NMR. The effect of reaction parameters on the condensation reaction of 9-fluorenone and phenol was investigated by univariate opti-mization. The optimal reaction conditions were obtained as follows: n(phenol): n(9-fluorenone): n(IL1)=6:1:0.125, n(IL1): n(thioglycolic acid)=5:2, reaction temperature 110℃ and reaction time 6 h. The catalytic effects of the four catalysts in the synthesis of bisphenolfluorene were investigated under the above conditions. For IL1, L IL2 and IL4 catalysts, the conversion of 9-fluorenone was 100%, and the selectivity of bisphenolfluorene was nearly 87%. In addition, the catalytic effect of ionic liquid IL1 was not significantly reduced after 5 consecutive uses.