In order to evaluate the spatial and temporal variation of N2O and associated flux into the air in a granite unconfined aquifer of Ikuchi Island, water samples were collected from 9 observation wells with different depths and 6 observation wells in the groundwater discharge area from 2013 to 2015 and analyzed for N2O, NO3--N and Cl-. The results showed that the concentrations of dissolved N2O changed with water depth, which can be attributed to the C/N ratio. When the C/N ratio ≤5, high concentrations of dissolved N2O occur. In addition, the N2O concentrations increased with the redox condition of water changes from oxidation to reductive. However, when water was in strong reductive conditions such as ORP ≤-200mV, the relative low concentrations of N2O took place, since N2O can change into N2 due to the complete denitrification. Dissolved N2O concentrations also increased in dry seasons, when most of observation wells being in a reductive state. In the groundwater discharge area, dissolved N2O and NO3--N concentrations decreased along the groundwater flow pathway, which results from the dilution of seawater and denitrification. The flux of N2O into air was estimated to be 49gha-1year-1, the same level as seawater emission rate. Whereas, in a high precipitation event(precipitation ≤ 30mm/day), 5gha-1day-1 (about 10 percent of annual N2O emission) would emission into air.