A series of sulfonic functionalized ionic liquids (SFILs) with different acidity were designed and prepared for the synthesis of terpene esters (e.g. geranyl acetate). The effect of acidity of SFILs on their performance was investigated systematically. It is found that tuning the acidity of SFILs to an appropriate value results in not only high conversion of geraniol but also superior selectivity of geranyl acetate. The SFILs can be easily separated from products by filtration under room temperature, thus showing good reusability. Furthermore, the kinetics for SFILs in the esterification of geraniol were determined as the basis for future process design.