In order to understand the product inhibition of enzymatic lignocellulose hydrolysis, the enzymatic hydrolysis of pretreated rice straw was carried out over an enzyme loading range of 2 to 30 FPU/g substrate, and the inhibition of enzymatic hydrolysis was analyzed kinetically based on the reducing sugars produced. It was shown that glucose, xylose, and arabinose were the main reducing sugar components contained in the hydrolysate. The mass ratio of glucose, xylose, and arabinose to the total reducing sugars was almost constant at 52.0%, 29.7% and 18.8%, respectively, in the enzyme loading range. The reducing sugars exerted competitive inhibitory interferences to the enzymatic hydrolysis. Glucose, xylose, and arabinose had a dissociation constant of 1.24, 0.54 and 0.33 g/l, respectively. The inhibitory interferences by reducing sugars were superimposed on the enzymatic hydrolysis. The enzymatic hydrolysis could be improved by the removal of the produced reducing sugars from hydrolysate.