Cities are increasingly being recognized as important contributors in global warming, for example by increasing atmospheric nitrous oxide (N₂O). However, urban ecosystems remain poorly understood due to their functional complexity. Further, few studies have documented the microbial processes governing the N₂O emissions from urban soils. Here, a field study was performed to assess in situ N₂O emissions in an urban and agricultural soil located in Xiamen, China. The mechanisms underlying the difference in N₂O emission patterns in both soils were further explored in an incubation experiment. Field investigations showed that N₂O emission (3.5–19.0 μg N₂O-N m^-2 h^-1) from the urban soil was significantly lower than that from the agricultural soil (25.4-18,502.3 μg N₂O-N m^-2 h^-1). Incubation experiments showed that the urban soil initially emitted lower denitrification-derived N₂O because of the lower nirS (encoding nitrite reductases) abundances, whereas overall N₂O accumulation during the incubation was mainly controlled by the initial nitrate content in soil. Nitrate addition in a short period (5 days) did not change the total bacterial and denitrifier abundances or the soil bacterial community composition, but significantly altered the relative distribution of some key genera capable of denitrification. Although the urban soil exhibited lower N₂O emission than its agricultural counterpart in this study, the expanding urban green areas should be taken into account when building N₂O emission reduction targets.