Effect of organic loading rate (OLR) on the continuous biological H-2 production from pretreated rice straw waste using a mesophilic up-flow anaerobic reactor (UAR) was investigated for 140d. OLR was varied from 7.1 to 26 g COD/l d. H-2 yield was significantly increased from 95.5 to 117 mmol/d, when OLR was largely increased from 7.1 to 21.4 g COD/l d, respectively. However, further increase in OLR up to 26 g COD/ld, showed a decreasing trend to 107.1 mmol/d. Likewise, H-2 production increased with OLR at the range of 7.1-21.4 g COD/ld, and reached the maximum H-2 production of 2.61/d. However, the H-2 production started to decrease with the further increase of OLR, and dropped to 2.21/d at OLR of 26 g COD/ld. The COD and carbohydrate removal efficiency were over 70% and 80% at OLRs of 7.1-21.4 g COD/ld, and decreased thereafter. (C) 2011 Elsevier Ltd. All rights reserved.