This paper evaluated the results of a field test for grou ndwater remediation by in-situ bioremediation at a site contaminated by tetrachloroethylene. The technique carried out in this test uses reductive dechlorination of contaminant in a subsurface environment. In the observation well during the field test, the percentages of daughter products like dichloroethylenes were observed to increase with the rise in reductive condition of the aquifer. Moreover, it was shown that the first order rate constants of all substances became greater than those of natural groundwater by more than a few orders. This meant that the reductive dechlorinataions could be accelerated during the field test.