During the dairy manure composting process, significant nitrous oxide (N 2 O) emissions occur just after the pile turnings. To understand the characteristics of this N 2 O emission, samples were taken from the compost surface and core independently, and the N 2 O production was monitored in laboratory incubation experiments. Equal amounts of surface and core samples were mixed to simulate the turning, and the 15 N isotope ratios within the molecules of produced N 2 O were analyzed by isotopomer analysis. The results showed that the surface samples emitted significant levels of N 2 O, and these emissions were correlated with NO x − -N accumulation. Moreover, the surface samples and surface-core mixed samples incubated at 30°C produced N 2 O with a low site preference (SP) value (−0.9 to 7.0‰) that was close to bacteria denitrification (0‰), indicating that denitrifiers in the surface samples are responsible for this N 2 O production. On the other hand, N 2 O produced by NO 2 − -amended core samples and surface samples incubated at 60°C showed unrecognized isotopic signatures (SP=11.4–20.3‰). From these results, it was revealed that the N 2 O production occurring just after the turnings was mainly derived from bacterial denitrification (including nitrifier denitrification) of NO x − -N under mesophilic conditions, and surface denitrifying bacteria appeared to be the main contributor to this process.