A new hydrogen-producing bacterium was isolated from the intestine of wild carp (Cyprinus carpio L.) of the Tarim River Basin. The isolate was identified as Klebsiella sp. based on 16S rDNA gene sequencing and examination of physiological and biochemical characteristics. The isolated strain, Klebsiella sp. WL1316, could effectively produce a high yield of hydrogen by using cotton stalk hydrolysate as substrate. The optimum fermentation conditions for hydrogen production were determined as follows: an initial sugar concentration of 40 g/L, a fermentation temperature of 37 A degrees C and an initial pH value of 8.0. The scaled-up fermentation process was conducted in a 5-L fermenter using these parameters. Higher productivities with maximum daily hydrogen production of 937.0 +/- 41.0 mL L-1 day(-1), cumulative hydrogen production of 2908.5 +/- 47.4 mL L-1, viable cell count of (20.2 +/- 0.6) x 10(8) CFU mL(-1) and hydrogen yield of 1.44 +/- 0.08 mol mol(-1)sugar(consumed) were obtained. The cumulative hydrogen production was predicted by the modified Gompertz equation with R (2) of 0.997, and values of R (m) and P were 44.8 mL L-1 h(-1) and 3057.6 mL L-1, respectively. These results indicated that the strain Klebsiella sp. WL1316 resulted in a high hydrogen production rate (HPR) and good hydrogen production potential. Moreover, this strain exhibited higher values of maximum hydrogen yield and HPR than the reported pure cultures.