This study investigates the usability of sewage sludge, waste from a waste water treatment facility, at the stable thermophilic temperature and different pH conditions in the biohydrogen production by dark fermentation. Without the addition of a pure hydrogen producer and nutrient source, the effect of a different constant pH in the range of pH 4-9 on biohydrogen production using sewage sludge was compared with that of a different initial pH. It was understood from the results that biohydrogen production varies according to the characterization of sewage sludge. In the experiments, the lag time was insignificant ((similar to)2 h). The maximum hydrogen production was achieved at pH 5 within the first 24-30 hours of fermentation (92894 mL m(-3) H-2). Therefore, it was determined that the higher digestion efficiencies of the sewage sludge were obtained at pH 5. In general, with the increase in methanogens in the medium, the hydrogen producing ability and hydrogen content of the sewage sludge gradually decreased. Hydrogen production at almost all the pH values after the third day was less than 1000 mL m(-3).