This experiment was conducted to measure concentration of dissolved N_2O in ground-water of 59 wells and to make emission factor for assessment of indirect N_2O emission at agricultural sector in agricultural areas of Gyeongnam province from 2007 to 2010. Concentrations of dissolved N_2O in ground-water of 59 wells were ranged trace to 196.6 μg-N L^-1. N2_O concentrations were positively related with NO_3-N suggesting that denitrification was the principal reason of N_2O production and NO_3-N concentration was the best predictor of indirect N_2O emission. The ratio of dissolved N_2O-N to NO_3-N in ground-water was very important to make emission factor for assessment of indirect N_2O emission at agricultural sector. The mean ratio of N_2O-N to NO_3-N was 0.0035. It was greatly lower than 0.015, the default value of currently using in the Intergovernmental Panel on Climate Change (IPCC) methodology for assessing indirect N_2O emission in agro-ecosystems (IPCC, 1996). It means that the IPCC’s present nitrogen indirect emission factor (EF5-g, 0.015) and indirect N_2O emission estimated with IPCC’s emission factor are too high to use adopt in Korea. So we recommend 0.0034 as national specific emission factor (EF_(5-g)) for assessment of indirect N_2O emission at agricultural sector. Using the estimated value of 0.0034 as the emission factor (EF_(5-g)) revised the indirect N_2O emission from agricultural sector in Korea decreased from 1,801,576 ton (CO_2-eq) to 964,645 ton (CO_2-eq) in 2008. The results of this study suggest that the indirect Emission of nitrous oxide from upland recommend 0.0034 as national specific emission factor (EF5-g) for assessment of indirect N_2O emission at agricultural sector.