Heteropolyacids (H 3 PW 12 O 40 , H 4 SiW 12 O 40 ) and salts of metal cations (M n+ ) and PW 12 O 40 3-(M 3/n PW 12 O 40 ) act as effective homogeneous catalysts for selective hydrolysis of cellobiose and cellulose to glucose and total reducing sugars (TRS), respectively, in an aqueous phase. For Brønsted acid catalysts, including mineral acid and heteropolyacids, the activity for both reactions increases with a decrease in the deprotonation enthalpies (DPE), indicating that stronger Brønsted acidity is more favorable. For M 3/n PW 12 O 40 of 11 kinds of metal ions