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Soil aggregation influences conservation and mineralization of carbon (C) and nitrogen (N), but aggregate separation method may influence levels of aggregate size distribution and quantification of C and N pools. Aggregate size distribution and soil organic C, soil total N, particulate organic C and N, microbial biomass C and N, potential C and N mineralization, NH4-N, and NO3-N concentrations in aggregates separated by dry and wet sieving methods were compared. The potential C and N mineralization, and microbial biomass C and N are considered as active pools, soil organic C and soil total N as slow pools, particulate organic C and N 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 the northern Great Plains. Aggregate amount was higher in dry than in wet sieving in the 4.75- to 2.00-mm size class, but the amount was higher in wet than in dry sieving in the 2.00- to 0.25-mm class in all sites, except in Sidney. In cultivated soil, no definite trends in C pools in aggregates were observed between sieving methods. In no-till grassland soil, C pools were higher in dry than in wet sieving in the less than 0.25-mm fractions, but the trend reversed in the greater than 2.00-mm fractions. In all fractions, active and available N pools were 2- to 30-fold higher in dry than in wet sieving probably because of loss of water-soluble N during wet sieving. Both C and N pools, except active C pools, in aggregates were usually higher in the less than 0.25-mm than in the other fractions, regardless of sieving methods. Aggregate size distribution and C and N pools determined by dry and wet sieving were well correlated, except for active N pools. Dry sieving of moist soil (water content around 25% field capacity) can be used as a rapid and reliable method of separating soil aggregates for determining C and N pools compared with wet sieving, which reduces microbial activities and N mineralization because of the destruction of physical habitat of microbial communities in aggregates and excludes water-soluble C and N pools.