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Graphical abstract We prepared the catalysts through the ion-exchange of natural calcium montmorillonite with an aqueous aluminum trichloride solution. Al3+ was a good Lewis acid catalyzing the isomerization of glucose to fructose, and the partially hydrolyzed Al−OH groups acted as Brønsted acid for the dehydration of fructose to HMF, which can be extracted by THF with a high yield. Highlights • A series of Al-mont-n were prepared with ion-exchange method for conversion of carbohydrates to HMF. • The catalytic activity is dependent on the concentrations of Al3+ ion. • A high yield of HMF (80.4%) was produced from glucose. • 60.1% and 81.6% yield of HMF were obtained from the dehydration of starch and inulin, respectively. Abstract Aluminum ion-exchanged Ca-montmorillonite with different concentrations of aluminum ion were prepared and applied in the conversion of carbohydrates to 5-hydroxymethylfurfural (HMF). It was found that two types of acid sites were present in the catalyst, Lewis acid sites for isomerization of glucose and Brønsted acid sites for dehydration of fructose. With Al-mont-10 as catalyst, the yield of HMF converted from glucose was 80.4% in a biphase system (THF: NaCl solution) at 180 °C for 2.5 h. Further, the catalyst also shows excellent catalytic performance in the conversion of starch and inulin, and the yield of HMF reached 60.1% and 81.6% under identical conditions, respectively. [ABSTRACT FROM AUTHOR]