Activated carbon supported polyoxometalates (AC-POMs) were used for acceleration of hydrolysis of biomass under microwave irradiation. Microwaves exhibited a higher saccharification rate for cellobiose and green seaweed (Monostroma latissimum) over AC-POMs than conductive heating by 1.25 to 1.55-fold. The activity of the AC-POMs was positively correlated with the dielectric loss of the catalysts, suggesting that microwave susceptibility of AC-POMs is relevant to the enhancement of catalysis under microwave irradiation.