Abstract: Strain HP1 was isolated from sediment and identified as Pseudomonas alcaligenes.A test was carried out to determine effects of carbon source and C/N ratio on denitrification of pure culture.Results show that carbon source had little effect on nitrate reductase activity,but obvious effect on nitrous oxide reductase activity.The optimal C/N ratio was 8 in batch denitrification tests,and with C/N ratios being<8 or >8,the N₂O concentration was lower under the condition of acetylene inhibition.The study show that Strain HP1 could grow with nitrate as its sole nitrogen source.It was confirmed that nitrate was partly consumed as nitrogen source when denitrification was carried out,and Strain HP1 had two kinds of nitrate reductase at least.There were a lot of intermediates accumulated in continuous culture at different C/N ratio,such as nitrite,ammonium.Temperature had effect on the accumulation of intermediates.Nitrite accumulated at C/N ratio of 3 but no nitrite accumulated at C/N ratio of 20.The objective of the present study was to provide methods for subsequent research.