Clostridium thermocellum ATCC 27405 was used to degrade sugarcane bagasse (SCB) directly for hydrogen production, which was significantly enhanced by supplementing medium with CaCO3. The effect of CaCO3 concentration on the hydrogen production was investigated. The hydrogen production was significantly enhanced with the CaCO3 concentration increased from 10 mM to 20 mM. However, with the CaCO3 concentration further increased from 20 mM to 100 mM, the hydrogen production didn't increase further. Under the optimal CaCO3 concentration of 20 mM, the hydrogen production reached 97.83 +/- 5.19 mmol/L from 2% sodium hydroxide-pretreated SCB, a 116.72% increase over the control (45.14 +/- 1.03 mmol/L), and the yield of hydrogen production reached 4.89 mmol H-2/g SCBadded. Additionally, CaCO3 promoted the biodegradation of SCB and the growth of C. thermocellum. The stimulatory effects of CaCO3 on biohydrogen production are mainly attributed to the buffering capacity of carbonate. The study provides a novel strategy to enhance biohydrogen production from lignocellulose. (C) 2015 Elsevier Ltd. All rights reserved.