Effect of nitrogen-load condition on hydrogen (H2) production and bacterial community in a continuous anaerobic hydrogen fermentation were investigated. The slight H2 production on extremely low nitrogen-load condition (C/N ratio: 180) at the start-up period. The highest H2 production was obtained when the C/N ratio was 36, the H2 production yield (mol-H2 / mol-glucose) reached to 1.7, and it was indicated that Clostridium pasteurianum mainly contributed to the H2 production. The H2 production was decreased on both the lower (C/N: 72) and higher (C/N: 18) nitrogen-load conditions. The excess nitrogen-load was not always suitable for the hydrogen production. The fluctuation of H2 production seemed to be caused by a change in the bacterial community according to the nitrogen-load condition, while a recovery of H2 productivity was possible by a control of nitrogen-load condition through the bacterial community change. When the nitrogen-load condition was not suitable for hydrogen production, the lactic acid concentration was increased and also lactic acid bacteria were definitely detected, which suggested that the competition between hydrogen fermentator and lactic acid producer was occurred. These results demonstrated that the nitrogen-load condition affect on the H2 productivity through the change of bacterial community in anaerobic hydrogen fermentation. Keyword : Hydrogen fermentation, Nitrogen load, Bacterial community, DGGE