AbstractFour organic Lewis acids, samarium(III), aluminum(III), yttrium(III), and indium(III) trifluoromethanesulfonates were combined with four organic Brønsted acids, benzenesulfonic, toluene-p-sulfonic, trichloroacetic, and oxalic acids to synergistically catalyze the decomposition of glucose to produce levulinic acid (LA). The combination of aluminum trifluoro-methanesulfonate (Al(CF3SO3)3) and oxalic acid (H2C2O4) exhibited a strong synergic activity for the decomposition of glucose to LA. The effects of the mole fraction of Al(CF3SO3)3 in the Al(CF3SO3)3-H2C2O4 system on the decompositions of glucose, fructose, and 5-hydroxymethylfurfural (5-HMF) were investigated. The mixed-acid system showed the strongest synergic catalytic activity for glucose, fructose, and 5-HMF decompositions at the Al(CF3SO3)3 mole fraction of 0.33. The effect of temperature on the decomposition of glucose in the Al(CF3SO3)3-H2C2O4 system was also investigated. Based on the results obtained in this contribution and previous work, synergy in catalytic systems was demonstrated.