Here we report N2O emission results for freshwater marshes isolated from human activities at the Sanjiang Experimental Station of Marsh Wetland Ecology in northeastern China. These results are important for us to understand N2O emission in natural processes in undisturbed freshwater marsh. Two adjacent plots of Deyeuxia angustifolia freshwater marsh with different water regimes, i.e., seasonally waterlogged (SW) and not- waterlogged (NW), were chosen for gas sampling, and soil and biomass studies. Emissions of N2O from NW plots were obviously higher than from the SW plots. Daily maximum N2O flux was observed at 13 o'clock and the seasonal maximum occurred in end July to early August. The annual average N2O emissions from the NW marsh were 4.45 μg m-2 h-1 in 2002 and 6.85 μg m-2 h-1 in 2003 during growing season. The SW marsh was overall a sink for N2O with corresponding annual emissions of -1.00 μg m-2 h-1 for 2002 and -0.76 μg m-2 h-1 for 2003. There were significant correlations between N2O fluxes and temperatures of both air and 5-cm-depth soil. The range of soil redox potential 200-400 mV appeared to be optimum for N2O flux. Besides temperature and plant biomass, the freeze-thaw process is also an important factor for N2O emission burst. Our results show that the freshwater marsh isolated from human activity in northeastern China is not a major source of N2O.