The one-pot dehydration/hydrolysis of mono- and disaccharides to 5-hydroxymethylfurfural (HMF) in the presence of several imidazolium ionic liquids was efficiently performed. The study aims to make a mechanistic insights on the direct transformation of sugars to HMF, including glucose, fructose, galactose, sucrose, maltose and lactose. With the catalyst of [NMP][HSO4], a HMF yield of 87 % was achieved from sucrose. In addition, [AMIM]Cl revealed a remarkable catalytic activity for the transformation of fructose to HMF without other catalyst or co-solvent and the yield of HMF was 91.1 %. Theoretical calculation results showed that [AMIM]Cl expressed a more efficient catalytic activity than [BMIM]Cl.