Aggregation influence conservation and mineralization of soil C and N but aggregate separation method may influence levels of aggregate amount and C and N pools. We compared aggregate amount and soil organic C (SOC), soil total N (STN), particulate organic C and N (POC and PON), microbial biomass C and N (MBC and MBN), potential C and N mineralization (PCM and PNM), NH₄-N, and NO₃-N concentrations in aggregates separated by dry and wet sieving methods. The PCM, PNM, MBC, and MBN are considered as active pools, SOC and STN as slow pools, POC and PON as intermediate pools, and NH₄-N and NO₃-N as available pools. Aggregate separation was made in soil samples from 0 to 5 and 5 to 20 cm depths with various properties and cropping systems in eastern Montana and western North Dakota. Aggregate amount was higher in dry than in wet sieving in 4.75- to 2.00-mm size class but the amount varied between sieving methods in other size classes. In cultivated soil, no definite trends in C pools were observed between aggregate size classes and sieving methods. In no-till grassland soil, C pools were higher in <0.25 mm than in 4.75-2.00 mm aggregates in dry sieving method but the trend reversed in wet sieving method. Nitrogen pools in aggregates were higher in <0.25 mm than in other size classes, regardless of sieving methods. In all aggregates, active and available N pools were 2- to 30-fold higher in dry than in wet sieving method. Dry sieving of moist soil can be a rapid and reliable method of determining soil aggregation and C and N pools compared with wet sieving which increases the destruction physical habitat of microbial habitats in aggregates and limits the determination of water soluble C and N pools.