Denitrification potentials vary according to the land uses, however, few studies were conducted in unmanaged agricultural land, despite its increasing area within Japan. We compared the denitrification potential of soils sampled from a managed and a two-years unmanaged grassland in Hokkaido by acetylene block method. We hypothesized that denitrification potential in managed grassland with high nitrogen inputs as fertilizer is relatively higher. The denitrification potentials were significantly different among the sites (ranged from 176 to 387 ng N₂O-N g soil^-1 h^-1), but land use effects were not observed. Also, the denitrification potentials were not affected by either soil properties (pH, WFPS, and CN ratio) or 16S rRNA based bacterial communities based on NMDS analysis. We also conducted denitrifier isolation tests and identified 16 genera. We found Nissabacter sp., which was recently discovered bacteria from pustule scalp. The other identified species such as Serratia sp. and Klebisiella sp. are ubiquitous denitrifiers. Rhodanobacter sp. were also found and they are often found and involved in denitrification at low pH. We might conclude that the denitrification potentials were mainly mediated by individual bacteria rather than soil properties or bacterial community in this study, although we need to further investigate this hypothesis.