Al-based solid acids supported on montmorillonite (SO42-/Al-O-MMT) were prepared by impregnation method. The catalytic performance of esterification reactions towards acetic acid with n-butanol and citric acid with n-butanol were investigated. The as-prepared catalysts were characterized by XRD, IR, TG-DSC, SEM, BET and Py-FTIR. The synthesis conditions and reaction parameters of esterification reactions were optimized in details as well. The experimental results showed that the catalytic activity of Al-based solid acids supported on montmorillonite has been greatly improved. TheSO42-/Al-O-MMTsolid acid catalyst showed optimal catalytic activities with 99.7% conversion of acetic acid and 96.1% conversion of citric acid when the calcination temperature was 400 °C and the impregnation concentration was 0.75 mol/L. Moreover, the SO42-/Al-O-MMTsolid acid catalyst maintained its high activity with above 89.0% conversion of acetic acid and 84.6% conversion of citric acid after being used for six times, which indicated that the SO42-/Al-O-MMTsolid acid catalyst showed great stability.