The purposes of this study are to investigate the formation and accumulation of extra-cellular polymers (ECP) by hydrogen utilizing anaerobes under high hydrogen partial pressure conditions, which are found at bottom parts of UASB reactors. Two types of enrichment culture were obtained in which hydrogen gas was intermittently replenished as a substrate with and without sulfates. One of them is an enrichment culture of hydrogen utilizing methanogen (HUM) and the other is a mixed culture of HUM and hydrogen utilizing sulfate reducing bacteria (SRB). Effects of ammonium nitrogen and cysteine on ECP formation were investigated for each culture. A remarkable accumulation of ECP by HUM was observed at the beginning of a batch experiment. in which hydrogen gas and ammonium nitrogen were sufficiently added without cysteine. However, ECPs were not significantly accumulated in the other cases for the HUM culture and all the cases for SRB. Chemical analysis of the produced ECP suggests that ECP protein was more dominant than ECP carbohydrate. HUMs played a role in producing ECP under such a special condition as well as acid producing bacteria. The experimental results suggest that ECP formation from HUM might contribute to self-granulation of sludge in UASB reactors at the bottom where high hydrogen partial pressure was established. There is also a possibility that SRB had a negative effect on sludge granulation by suppressing ECP accumulation.