Repeated batch cultivation was applied to enrich hydrogen fermentative microflora under extreme-thermophilic (70A degrees C) environment. Initial inoculums received from a hydrogen producing reactor fed with organic fraction of household solid wastes. In total seven transfers was conducted and maximum hydrogen yield reached 296 ml H-2/g (2.38 mol/mol) glucose and 252 ml H-2/g (2.03 mol/mol) for 1 and 2 g/l glucose medium, respectively. It was found that hydrogen production was firstly decreased and got increased gradually from third generation. Acetate was found to be the main metabolic by-product in all batch cultivation. Furthermore, the diversity of bacterial community got decreased after repeated batch cultivation. It was proved that repeated batch cultivation was a good method to enhance the hydrogen production by enriching the mixed cultures of dominant species.