An integration process to produce biohydrogen by rice straw hydrolysate and anaerobic fermentation was proposed in this study. The rice straw was used as the raw material to generate reducing sugar (RS) for the anaerobic fermentation to produce biohydrogen. During the hydrolysis process, the ratio of water:biomass:acid equals to 100:30:0.9 at 150 degrees C for 1 h. Sulfuric acid, nitric acid, hydrochloric acid, and deionized water (no acid added) were used as the catalyst and the chemical oxygen demand (reducing sugar, g/L) of the hydrolysates was 69.84 (36.70), 83.90 (63.4), 74.64 (66.37), and 31.67 (3.17) g COD/L. Overliming treatment by Ca(OH)(2) and activated carbon was used to remove the suppressors, such as the acetic acid and furfural, in the hydrolysate and the treated hydrolysate was used for biohydrogen production. At the initial reaction condition of 40 degrees C, 150 rpm, pH = 6.5, and RS concentration = 3 g/L under 60 mL working volume in a 200 mL bottle, the maximum hydrogen yield without/with Endo solution (in mmol H(2)/g-rice straw) were 0.00260/0.00160 (no acid), 0.191/0.105 (H(2)SO(4) catalyzed), 0.305/0.177 (HCl catalyzed), and 0.291/0.285 (HNO(3) catalyzed), respectively. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.