The fermentative hydrogen production capability of the newly isolated Clostridium sp. 6A-5 bacterium was studied in a batch cultivation experiment. Various culture conditions (temperature, initial pH, and glucose concentration) were evaluated for their effects on cell growth and hydrogen production (including the yield and rate) of Clostridium sp. 6A-5. Optimal cell growth was observed at 40 degrees C, initial pH 7.5-8, and glucose concentration 16-26 g/L. The optimal hydrogen yield was obtained at 43 degrees C, initial pH 8, and glucose concentration 10-16 g/L. Hydrogen began to evolve when cell growth entered the mid-exponential phase and reached the maximum production rate at the late exponential and stationary phases. The maximum hydrogen yield, and rate were 2727 mL/L, and 269.3 mL H-2/L h, respectively. These results indicate that Clostridium sp. 6A-5 is a good candidate for mesophilic fermentative hydrogen production. (C) 2013 Published by Elsevier Ltd.