The effect of bacterial adhesion on powdered activated carbon on bacterial activity in non-toxic wastewater was studied and the difference of powdered activated carbon species on the stimulation of bacterial activity was also evaluated using eight kinds of powdered activated carbon. Pure cultures of Escherichia coli K-12, which can reduce NO3- to NO2- in anoxic conditions, were used. Specific nitrate reduction activity was used as an indicator of bacterial activity. The higher specific nitrate reduction rates were noted in cultures with powdered activated carbon than without powdered activated carbon or with Kaolin. The specific nitrate reduction rate with powdered activated carbon was up to about 1.4 times as highas those without powdered activated carbon. The stimulation of bacterial activity was induced by the adhesion of bacterial cells onto powdered activated carbon. There are powderedactivated carbons that can stimulate bacterial activity, whereas not all the powdered activated carbon can stimulate bacterial activity. Surface characteristics like Brunauer-Emmett-Teller specific surface areas, total surface acidity, oxygen functional groups, total surface basicity, surface charge, pH(pzc), iodine number, concentrations of metals, electric resistance, free radical concentration and adsorption capacity of formate did not related with the stimulation of the bacterial activity.