A series of heteropolyacid (HPA) ionic liquids [C₄H₆N₂(CH₂)₃SO₃H]_3−nH_nPW₁₂O₄₀ ([MIMPSH]_nH_3−nPW₁₂O₄₀, n = 1, 2 3, abbreviated as [MIMPSH]_nH_3−nPW) was used to catalyze one-pot depolymerization of cellulose into glucose. Their performances were much better than those of the previously reported HPAs, such as H₃PW₁₂O₄₀, Cs_2.5H_0.5PW₁₂O₄₀. Besides cellulose, the HPA ionic liquids were able to catalyze the conversion of sucrose and starch into glucose. In addition, one-pot synthesis of levulinic acid (LA) directly from cellulose was realized using these HPA ionic liquid catalysts in a water–methyl isobutyl ketone (MIBK) biphasic system. The separation of the products and catalysts was easy, and the retrieved [MIMPSH]_nH_3−nPW could be repeatedly used without appreciable loss of performance.