The N isotopic composition of nitrate in soil extraction samples can deliver critical information regarding the soil N cycle for biogeochemical processes. Here, we present a preparatory ion-exchange resin method for the N isotope analysis of NO3- in saturated CaSO4 soil extracts. This method showed that the NO3- in saturated CaSO4 soil extracts could be effectively separated from SO42- and other anions to avoid interference from the large amounts of coexisting anions in soil extracts. The nitrate recovery rate ranged from 95.54 to 105.04%. The resulting average natural abundance of N-15 (delta N-15) values of the KNO3 solutions and the KNO3-CaSO4 solutions were +6.04 +/- 0.03 parts per thousand (n = 6) and +6.03 +/- 0.12 parts per thousand (n = 6), respectively. The average delta N-15 value of the KNO3 salt was +6.07 +/- 0.06 parts per thousand (n = 12). Therefore, we concluded that N isotopic fractionation did not occur throughout the process. In addition, the delta N-15-NO3- values of natural soils extracted using saturated CaSO4 were reproducible between separate analytical runs. The standard deviations of the delta N-15-NO3- for the three different soils were +/- 0.17 parts per thousand (n = 4), +/- 0.04 parts per thousand (n = 3), and +/- 0.34 parts per thousand (n = 3). Our ion-exchange method was effective at separating NO3- from other anions in the soil extracts and was suitable for measuring the delta N-15-NO3 of saturated CaSO4 soil extracts.