The photocatalytic reaction of polyoxotungstate, [BW12O40]5- and [SiW12O40]4-, led to the generation of hydrogen gas from biomass such as a sugarcane juice and tapioca starch under irradiation of UV light. These photoreactions were investigated in the pH dependence. The results showed that hydrogen was obtained at 2<pH<4. The photolysis of [BW12O40]5- and [SiW12O40]4- in presence of 60 ml of sugarcane juice at pH 2 level were obtained 0.15 ml and 0.51 ml of hydrogen, respectively. Especially, it was observed that the photolysis of the starch evolved oxygen without any catalysts. The oxygen contents affected to the reduced species of polyoxotungstates. Each photoreaction exhibited a different behaviour for the dependence of the amounts of catalyst. Lowering amounts of [SiW12O40]4- produced much hydrogen at pH 2 level. In contrast, lowering amounts of [BW12O40]5- could not evolve much hydrogen due to the domination of reoxidation of the reduced species by oxygen.