Nitrifi cation inhibitors, such as dicyandiamide(DCD), have been shown to decrease leaching from urea- and ammoniumbased fertilizers in agricultural soils. The effect of nitrifi cation inhibitors on nitrifi er and denitrifi er in short- and long-term intensive vegetable cultivation soils was poorly understood. In this study, the pot trial was conducted to investigate the differential responses of nitrifi er(amoA-containing bacteria) and denitrifi er(nirK-containing bacteria) to DCD in short-(soil S) and long-term(soil L) intensive vegetable cultivation soils. Quantitative polymerase chain reaction(qPCR) and terminal restriction fragment length polymorphism(T-RFLP) were employed to detect the abundance and composition of amoA- and nirK-containing communities. The results indicated that application of DCD led to a consistently higher NH4+-N concentration during the whole incubation in soil L, while it was quickly decreased in soil S after 21 days. Furthermore, DCD induced more severe decrease of the abundance of amoA-containing bacteria in soil L than in soil S. However, the abundance of the nirKcontaining community was not signifi cantly affected by DCD in both soils. Long-term vegetable cultivation resulted in a super-dominant amoA-containing bacteria group and less divergence in soil L compared with soil S, and DCD did not cause obvious shifts of the composition of ammonia-oxidising bacteria(AOB). On the contrary, both amoA- and nirK-containing bacterial compositions were infl uenced by DCD in soil S. The results suggested that long-term intensive vegetable cultivation with heavy nitrogen fertilization resulted in signifi cant shifts of AOB community, and this community was sensitive to DCD, but denitrifi ers were not clearly affected by DCD. The effect of nitrifi cation inhibitors on nitrifier and denitrifier in short- and long-term intensive vegetable cultivation soils was this poorly understood. In this study, the pot trial was conducted to investigate the differential responses of nitrifier (amoA-containing bacteria) and denitrifier (nirK-containing bacteria) to DCD in short- (soil S) and long-term soil L) intensive vegetable cultivation soils. Quantitative polymerase chain reaction (qPCR) and terminal restriction fragment length polymorphism (T-RFLP) were employed to detect the abundance and composition of amoA- and nirK-containing communities. The results indicates that the application of DCD led to a consistently higher NH4 + -N concentration during the whole incubation in soil L, while it was quickly decreased in soil S after 21 days. DCD induced more severe dec rease of the abundance of amoA-containing bacteria in soil L than in soil S. However, the abundance of the nirK con- taining community was not signifi cantly affected by DCD in both soils. Long-term plant cultivation resulted in a super-dominant amoA-containing bacteria group and less divergence in soil L compared with soil S, and DCD did not cause obvious shifts of the composition of ammonia-oxidising bacteria (AOB). On the contrary, both amoA- and nirK-containing bacterial compositions were infuenced by DCD in soil S. The results suggested that long-term intensive vegetable cultivation with heavy nitrogen production resulted in signifi cant shifts of AOB community, and this community was sensitive to DCD, but denitrifi ers were not clearly affected by DCD.