【Objective】Variations in and unreliability of nitrogen transformation under heavy metal stress in coastal wetland ecosystems,caused by global warming and increasing anthropogenic activities,have drawn much attention. In this study,we aimed to examine the relative importance of denitrification (Den) and dissimilatory nitrate reduction to ammonium (DNRA) in sediments with various Cd contents.【Method】Sediment samples were obtained from under Phragmites australis,Spartina alterniflora community and mudflats without vegetation in the Chongming Dongtan wetlands. Den and DNRA rates in the sediments were measured using the ~(15)N isotope tracing technique after incubation with various concentrations of Cd. The effectiveness of Cd was evaluated using the modified BCR 3 step sequential extraction method.【Result 】Low doses of Cd (0.05-0.30 mg /kg) increased DNRA/Den values by 6.9%-53.4%,indicating nitrate reductions in sediments being induced mainly with DNRA pathway. In contrast,the ratios under Spartina alterniflora community were 3.1 to 5.4 times higher than those under Phragmites australis community. This suggests that Spartina alterniflora community may be beneficial for nitrate reductions via the DNRA pathway. In addition,Den and DNRA rates under Phragmites australis community were mainly dominated by exchangeable and reducible Cd in the sediments,whereas the content of oxidized Cd substantially affected the relative importance of Den and DNRA under Spartina alterniflora community. 【Conclusion】Low doses of Cd input in coastal wetlands probably stimulate nitrate reduction in sediments by enhancing the DNRA pathway. Cd fractions affecting Den and DNRA rates significantly depend on the vegetation type.