5-Hydroxymethylfurfural was converted to succinic anhydride in 90–92% yield by oxidation with 30% hydrogen peroxide using 10 mol% 1-(alkylsulfonic)-3-methylimidazolium chloride acidic ionic liquid catalysts at 60 °C for 14 h. The acidic ionic liquid catalyst could be reused for four catalytic cycles without appreciable loss in catalytic activity. On the other hand oxidation of furfural under similar ionic liquid catalyzed conditions produced a mixture of three products: 2(5H)-furanone, succinic anhydride and maleic acid in 68, 8 and 12% yields respectively.