A series of insoluble heteropolytungstate salts, CsxH3-xPW12O40 (x = 1-3), were prepared and applied to the selective hydrolysis of microcrystalline cellulose to sugars in the aqueous phase. CsxH3-xPW12O40 were active toward the hydrolysis of cellulose into total reducing sugars (TRS) and glucose, which are the important products for the application for biofuels. The conversion of cellulose and total yield for the main products increased with increasing acidity of the catalyst. Cs1H2PW12O40 exhibited the best catalytic activity in terms of the conversion of cellulose and yields for TRS and glucose, while Cs2.2H0.8PW12O40 showed the highest selectivity for TRS and glucose.