This article deals with numbers, compositions and enzyme activities of denitrifiers in paddy soil in Taihu Lake district. The results obtained are as follows. 1. The amount of denitrifiers teas rather numerous in paddy soil in this region, generally, more than million per gram of dry soil. Numbers of denitrifiers in soil with higher fertility were larger than that with lower fertility. In all the paddy soils, there was significant positive correlation between numbers of denitrifiers and bacteria. 2. The species in genus Bacillus and Pseudomonas were the predominant denitrifying bacteria in paddy soils in Taihu Lake district. The highest occurrence frequency of Bac. megotherium and Pseu. fluorecens has been found in these soils, they even constituted 10-50% of the total denitrifiers, while the frequencies of Bec. licheniformis and Bac. firmus were much lower than the former. 3. The enzyme activities of denitrifiers have been determined by means of GC-technique. The amount of the strains reducing NO₃^- to N₂O and those reducing N₂O to N₂ constituted 67% and 56% of the strains tested, respectively. The amount of denitrifiers being able to reduce ¹⁵NO₃^- to ¹⁵NH₄⁺ through dissimilatory reduction pathway constituted 92% of the strains tested. The dissimilatory reduction ability of Bac. cereus and Bac. licheniformis were vigorous.